Down-integrate internal changes to github. (#5555)

* Down-integrate internal changes to github.

* fix python conformance test

* fix csharp conformance test

* add back java map_lite_test.proto's optimize for option

* fix php conformance test
diff --git a/conformance/conformance.proto b/conformance/conformance.proto
index b0dc762..91e2ad3 100644
--- a/conformance/conformance.proto
+++ b/conformance/conformance.proto
@@ -61,7 +61,7 @@
 enum TestCategory {
   UNSPECIFIED_TEST = 0;
   BINARY_TEST = 1;  // Test binary wire format.
-  JSON_TEST = 2;  // Test json wire format.
+  JSON_TEST = 2;    // Test json wire format.
   // Similar to JSON_TEST. However, during parsing json, testee should ignore
   // unknown fields. This feature is optional. Each implementation can descide
   // whether to support it.  See
@@ -72,6 +72,10 @@
                   // Opensource testees just skip it.
 }
 
+message FailureSet {
+  repeated string failure = 1;
+}
+
 // Represents a single test case's input.  The testee should:
 //
 //   1. parse this proto (which should always succeed)