metrics: explicitly specify source_set generator for all metric protos

This fixes the build on iOS in Chromium.

Change-Id: I7cc3a0f94b6963169131b7a6940dbd2a55ad25c7
diff --git a/gn/proto_library.gni b/gn/proto_library.gni
index cf0a869..9638737 100644
--- a/gn/proto_library.gni
+++ b/gn/proto_library.gni
@@ -309,7 +309,10 @@
       }
 
       # Not needed for source_set proto_library target.
-      not_needed([ "propagate_imports_configs_" ])
+      not_needed([
+                   "propagate_imports_configs_",
+                   "proto_path",
+                 ])
     } else {
       assert(false, "Invalid 'proto_generators' value.")
     }
diff --git a/protos/perfetto/metrics/BUILD.gn b/protos/perfetto/metrics/BUILD.gn
index 0b8aa44..a0aec35 100644
--- a/protos/perfetto/metrics/BUILD.gn
+++ b/protos/perfetto/metrics/BUILD.gn
@@ -16,11 +16,16 @@
 import("../../../gn/proto_library.gni")
 
 perfetto_proto_library("@TYPE@") {
+  proto_generators = [
+    "lite",
+    "source_set",
+  ]
   deps = [ "android:@TYPE@" ]
   sources = [ "metrics.proto" ]
 }
 
 perfetto_proto_library("custom_options_@TYPE@") {
+  proto_generators = [ "source_set" ]
   sources = [ "custom_options.proto" ]
   import_dirs = [ "${perfetto_protobuf_src_dir}" ]
 }
diff --git a/protos/perfetto/metrics/android/BUILD.gn b/protos/perfetto/metrics/android/BUILD.gn
index eaa2649..e814a80 100644
--- a/protos/perfetto/metrics/android/BUILD.gn
+++ b/protos/perfetto/metrics/android/BUILD.gn
@@ -15,6 +15,10 @@
 import("../../../../gn/proto_library.gni")
 
 perfetto_proto_library("@TYPE@") {
+  proto_generators = [
+    "lite",
+    "source_set",
+  ]
   sources = [
     "batt_metric.proto",
     "cpu_metric.proto",
diff --git a/protos/perfetto/metrics/chrome/BUILD.gn b/protos/perfetto/metrics/chrome/BUILD.gn
index 9eff20d..6287d8c 100644
--- a/protos/perfetto/metrics/chrome/BUILD.gn
+++ b/protos/perfetto/metrics/chrome/BUILD.gn
@@ -15,10 +15,7 @@
 import("../../../../gn/proto_library.gni")
 
 perfetto_proto_library("@TYPE@") {
-  proto_generators = [
-    "zero",
-    "source_set",
-  ]
+  proto_generators = [ "source_set" ]
   deps = [
     "..:@TYPE@",
     "..:custom_options_@TYPE@",