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

build/perf_critical.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.
+#
+# This file enables hard optimizations on a per-target basis, it needs to be
+# included inside targets that require the absolute best performance.
+# This currently affects only the official Windows build, where it turns on
+# whole program optimizations for all sources compiled by the target.
+{
+  'conditions': [
+    ['buildtype=="Official"', {
+        'msvs_settings': {
+          'VCCLCompilerTool': {
+            'WholeProgramOptimization': 'true',
+          },
+        },
+      },
+    ],
+  ],
+}