Added finch experiment to track new menu style effect.

ui/native_theme/native_theme.cc

 // Copyright (c) 2012 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.
 
 #include "ui/native_theme/native_theme.h"
 
 #include "base/command_line.h"
+#include "base/metrics/field_trial.h"
 #include "ui/base/ui_base_switches.h"
 
+// Constants for the new menu style field trial.
+const char kNewMenuStyleFieldTrialName[] = "NewMenuStyle";
+const char kNewMenuStyleFieldTrialGroupName[] = "OldStyle";
+
 namespace ui {
 
 void NativeTheme::SetScrollbarColors(unsigned inactive_color,
                                      unsigned active_color,
                                      unsigned track_color) {
   thumb_inactive_color_ = inactive_color;
   thumb_active_color_ = active_color;
   track_color_ = track_color;
 }
 
 // NativeTheme::instance() is implemented in the platform specific source files,
 // such as native_theme_win.cc or native_theme_linux.cc
 
 // static
 bool NativeTheme::IsNewMenuStyleEnabled() {
   static bool enable_new_menu_style =
       !CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kDisableNewMenuStyle);
+  // Run experiment only if there is no kDisableNewMenuStyle flag.
+  if (enable_new_menu_style) {
+    enable_new_menu_style =
+        base::FieldTrialList::FindFullName(kNewMenuStyleFieldTrialName) !=
+        kNewMenuStyleFieldTrialGroupName;
+  }
   return enable_new_menu_style;
 }
 
 NativeTheme::NativeTheme()
     : thumb_inactive_color_(0xeaeaea),
       thumb_active_color_(0xf4f4f4),
       track_color_(0xd3d3d3) {
 }
 
 NativeTheme::~NativeTheme() {}
 
 }  // namespace ui