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

build/internal/release_defaults.gypi

+# 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',
     },
   },
 }