Allow targets to self-select optimization level in official builds.

build/internal/release_defaults.gypi

Index: build/internal/release_defaults.gypi
diff --git a/build/internal/release_defaults.gypi b/build/internal/release_defaults.gypi
index 7f1ddb8bec8aeb952eee41da97e0ab25ea9363e6..1bf674ac12165bdb7c56af4e5ef55c8cc7de76b6 100644
--- a/build/internal/release_defaults.gypi
+++ b/build/internal/release_defaults.gypi
@@ -1,11 +1,17 @@
+# Copyright (c) 2011 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
 {
   'msvs_settings': {
     'VCCLCompilerTool': {
       'StringPooling': 'true',
     },
     'VCLinkerTool': {
+      # No incremental linking.
       'LinkIncremental': '1',
+      # Eliminate Unreferenced Data (/OPT:REF).
       'OptimizeReferences': '2',
+      # Folding on (/OPT:ICF).
       'EnableCOMDATFolding': '2',
     },
   },