JavaScript: move extension binary info to separate struct.
diff --git a/js/commonjs/export.js b/js/commonjs/export.js
index a3cfbd6..23ae47f 100644
--- a/js/commonjs/export.js
+++ b/js/commonjs/export.js
@@ -9,12 +9,14 @@
 goog.require('jspb.BinaryReader');
 goog.require('jspb.BinaryWriter');
 goog.require('jspb.ExtensionFieldInfo');
+goog.require('jspb.ExtensionFieldBinaryInfo');
 goog.require('jspb.Message');
 
 exports.Message = jspb.Message;
 exports.BinaryReader = jspb.BinaryReader;
 exports.BinaryWriter = jspb.BinaryWriter;
 exports.ExtensionFieldInfo = jspb.ExtensionFieldInfo;
+exports.ExtensionFieldBinaryInfo = jspb.ExtensionFieldBinaryInfo;
 
 // These are used by generated code but should not be used directly by clients.
 exports.exportSymbol = goog.exportSymbol;
diff --git a/js/message.js b/js/message.js
index e8185de..f746ee6 100644
--- a/js/message.js
+++ b/js/message.js
@@ -35,6 +35,7 @@
  */
 
 goog.provide('jspb.ExtensionFieldInfo');
+goog.provide('jspb.ExtensionFieldBinaryInfo');
 goog.provide('jspb.Message');
 
 goog.require('goog.array');
@@ -84,19 +85,12 @@
  * @param {?function(new: jspb.Message, Array=)} ctor
  * @param {?function((boolean|undefined),!jspb.Message):!Object} toObjectFn
  * @param {number} isRepeated
- * @param {?function(number,?)=} opt_binaryReaderFn
- * @param {?function(number,?)|function(number,?,?,?,?,?)=} opt_binaryWriterFn
- * @param {?function(?,?)=} opt_binaryMessageSerializeFn
- * @param {?function(?,?)=} opt_binaryMessageDeserializeFn
- * @param {?boolean=} opt_isPacked
  * @constructor
  * @struct
  * @template T
  */
 jspb.ExtensionFieldInfo = function(fieldNumber, fieldName, ctor, toObjectFn,
-    isRepeated, opt_binaryReaderFn, opt_binaryWriterFn,
-    opt_binaryMessageSerializeFn, opt_binaryMessageDeserializeFn,
-    opt_isPacked) {
+    isRepeated) {
   /** @const */
   this.fieldIndex = fieldNumber;
   /** @const */
@@ -106,19 +100,36 @@
   /** @const */
   this.toObjectFn = toObjectFn;
   /** @const */
-  this.binaryReaderFn = opt_binaryReaderFn;
-  /** @const */
-  this.binaryWriterFn = opt_binaryWriterFn;
-  /** @const */
-  this.binaryMessageSerializeFn = opt_binaryMessageSerializeFn;
-  /** @const */
-  this.binaryMessageDeserializeFn = opt_binaryMessageDeserializeFn;
-  /** @const */
   this.isRepeated = isRepeated;
-  /** @const */
-  this.isPacked = opt_isPacked;
 };
 
+/**
+ * Stores binary-related information for a single extension field.
+ * @param {!jspb.ExtensionFieldInfo<T>} fieldInfo
+ * @param {?function(number,?)=} binaryReaderFn
+ * @param {?function(number,?)|function(number,?,?,?,?,?)=} binaryWriterFn
+ * @param {?function(?,?)=} opt_binaryMessageSerializeFn
+ * @param {?function(?,?)=} opt_binaryMessageDeserializeFn
+ * @param {?boolean=} opt_isPacked
+ * @constructor
+ * @struct
+ * @template T
+ */
+jspb.ExtensionFieldBinaryInfo = function(fieldInfo, binaryReaderFn, binaryWriterFn,
+    binaryMessageSerializeFn, binaryMessageDeserializeFn, isPacked) {
+  /** @const */
+  this.fieldInfo = fieldInfo;
+  /** @const */
+  this.binaryReaderFn = binaryReaderFn;
+  /** @const */
+  this.binaryWriterFn = binaryWriterFn;
+  /** @const */
+  this.binaryMessageSerializeFn = binaryMessageSerializeFn;
+  /** @const */
+  this.binaryMessageDeserializeFn = binaryMessageDeserializeFn;
+  /** @const */
+  this.isPacked = isPacked;
+};
 
 /**
  * @return {boolean} Does this field represent a sub Message?
@@ -491,11 +502,13 @@
 jspb.Message.serializeBinaryExtensions = function(proto, writer, extensions,
     getExtensionFn) {
   for (var fieldNumber in extensions) {
-    var fieldInfo = extensions[fieldNumber];
+    var binaryFieldInfo = extensions[fieldNumber];
+    var fieldInfo = binaryFieldInfo.fieldInfo;
+
     // The old codegen doesn't add the extra fields to ExtensionFieldInfo, so we
     // need to gracefully error-out here rather than produce a null dereference
     // below.
-    if (!fieldInfo.binaryWriterFn) {
+    if (!binaryFieldInfo.binaryWriterFn) {
       throw new Error('Message extension present that was generated ' +
                       'without binary serialization support');
     }
@@ -508,16 +521,17 @@
         // message may require binary support, so we can *only* catch this error
         // here, at runtime (and this decoupled codegen is the whole point of
         // extensions!).
-        if (fieldInfo.binaryMessageSerializeFn) {
-          fieldInfo.binaryWriterFn.call(writer, fieldInfo.fieldIndex,
-              value, fieldInfo.binaryMessageSerializeFn);
+        if (binaryFieldInfo.binaryMessageSerializeFn) {
+          binaryFieldInfo.binaryWriterFn.call(writer, fieldInfo.fieldIndex,
+              value, binaryFieldInfo.binaryMessageSerializeFn);
         } else {
           throw new Error('Message extension present holding submessage ' +
                           'without binary support enabled, and message is ' +
                           'being serialized to binary format');
         }
       } else {
-        fieldInfo.binaryWriterFn.call(writer, fieldInfo.fieldIndex, value);
+        binaryFieldInfo.binaryWriterFn.call(
+            writer, fieldInfo.fieldIndex, value);
       }
     }
   }
@@ -535,12 +549,13 @@
  */
 jspb.Message.readBinaryExtension = function(msg, reader, extensions,
     getExtensionFn, setExtensionFn) {
-  var fieldInfo = extensions[reader.getFieldNumber()];
-  if (!fieldInfo) {
+  var binaryFieldInfo = extensions[reader.getFieldNumber()];
+  var fieldInfo = binaryFieldInfo.fieldInfo;
+  if (!binaryFieldInfo) {
     reader.skipField();
     return;
   }
-  if (!fieldInfo.binaryReaderFn) {
+  if (!binaryFieldInfo.binaryReaderFn) {
     throw new Error('Deserializing extension whose generated code does not ' +
                     'support binary format');
   }
@@ -548,14 +563,14 @@
   var value;
   if (fieldInfo.isMessageType()) {
     value = new fieldInfo.ctor();
-    fieldInfo.binaryReaderFn.call(
-        reader, value, fieldInfo.binaryMessageDeserializeFn);
+    binaryFieldInfo.binaryReaderFn.call(
+        reader, value, binaryFieldInfo.binaryMessageDeserializeFn);
   } else {
     // All other types.
-    value = fieldInfo.binaryReaderFn.call(reader);
+    value = binaryFieldInfo.binaryReaderFn.call(reader);
   }
 
-  if (fieldInfo.isRepeated && !fieldInfo.isPacked) {
+  if (fieldInfo.isRepeated && !binaryFieldInfo.isPacked) {
     var currentList = getExtensionFn.call(msg, fieldInfo);
     if (!currentList) {
       setExtensionFn.call(msg, fieldInfo, [value]);
diff --git a/src/google/protobuf/compiler/js/js_generator.cc b/src/google/protobuf/compiler/js/js_generator.cc
index e030066..d3852a9 100755
--- a/src/google/protobuf/compiler/js/js_generator.cc
+++ b/src/google/protobuf/compiler/js/js_generator.cc
@@ -2524,6 +2524,29 @@
         "$class$.extensions = {};\n"
         "\n",
         "class", GetPath(options, desc));
+
+    if (options.binary) {
+      printer->Print(
+          "\n"
+          "/**\n"
+          " * The extensions registered with this message class. This is a "
+          "map of\n"
+          " * extension field number to fieldInfo object.\n"
+          " *\n"
+          " * For example:\n"
+          " *     { 123: {fieldIndex: 123, fieldName: {my_field_name: 0}, "
+          "ctor: proto.example.MyMessage} }\n"
+          " *\n"
+          " * fieldName contains the JsCompiler renamed field name property "
+          "so that it\n"
+          " * works in OPTIMIZED mode.\n"
+          " *\n"
+          " * @type {!Object.<number, jspb.ExtensionFieldInfo>}\n"
+          " */\n"
+          "$class$.extensionsBinary = {};\n"
+          "\n",
+          "class", GetPath(options, desc));
+    }
   }
 }
 
@@ -2571,7 +2594,7 @@
       "    default:\n");
   if (IsExtendable(desc)) {
     printer->Print(
-        "      jspb.Message.readBinaryExtension(msg, reader, $extobj$,\n"
+        "      jspb.Message.readBinaryExtension(msg, reader, $extobj$Binary,\n"
         "        $class$.prototype.getExtension,\n"
         "        $class$.prototype.setExtension);\n"
         "      break;\n",
@@ -2705,8 +2728,8 @@
 
   if (IsExtendable(desc)) {
     printer->Print(
-        "  jspb.Message.serializeBinaryExtensions(this, writer, $extobj$,\n"
-        "    $class$.prototype.getExtension);\n",
+        "  jspb.Message.serializeBinaryExtensions(this, writer,\n"
+        "    $extobj$Binary, $class$.prototype.getExtension);\n",
         "extobj", JSExtensionsObjectName(options, desc->file(), desc),
         "class", GetPath(options, desc));
   }
@@ -2874,7 +2897,7 @@
       "     /** @type {?function((boolean|undefined),!jspb.Message=): "
       "!Object} */ (\n"
       "         $toObject$),\n"
-      "    $repeated$",
+      "    $repeated$);\n",
       "index", SimpleItoa(field->number()),
       "name", JSObjectFieldName(options, field),
       "ctor", (field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE ?
@@ -2886,12 +2909,18 @@
 
   if (options.binary) {
     printer->Print(
-        ",\n"
+        "\n"
+        "$extendName$Binary[$index$] = new jspb.ExtensionFieldBinaryInfo(\n"
+        "    $class$.$name$,\n"
         "    $binaryReaderFn$,\n"
         "    $binaryWriterFn$,\n"
         "    $binaryMessageSerializeFn$,\n"
-        "    $binaryMessageDeserializeFn$,\n"
-        "    $isPacked$);\n",
+        "    $binaryMessageDeserializeFn$,\n",
+        "extendName", JSExtensionsObjectName(options, field->file(),
+                                             field->containing_type()),
+        "index", SimpleItoa(field->number()),
+        "class", extension_scope,
+        "name", JSObjectFieldName(options, field),
         "binaryReaderFn", JSBinaryReaderMethodName(options, field),
         "binaryWriterFn", JSBinaryWriterMethodName(options, field),
         "binaryMessageSerializeFn",
@@ -2901,10 +2930,11 @@
         "binaryMessageDeserializeFn",
         (field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) ?
         (SubmessageTypeRef(options, field) +
-         ".deserializeBinaryFromReader") : "null",
+         ".deserializeBinaryFromReader") : "null");
+
+    printer->Print(
+        "    $isPacked$);\n",
         "isPacked", (field->is_packed() ? "true" : "false"));
-  } else {
-    printer->Print(");\n");
   }
 
   printer->Print(