Revert

chrome/browser/gpu/chrome_gpu_util.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 "chrome/browser/gpu/chrome_gpu_util.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/version.h"
@@ skipping 138 matching lines @@
   // Produce the same result on every run of this client.
   trial->UseOneTimeRandomization();
 
   base::FieldTrial::Probability force_compositing_mode_probability = 0;
   base::FieldTrial::Probability threaded_compositing_probability = 0;
 
   // Note: Threaded compositing mode isn't feature complete on mac or linux yet:
   // http://crbug.com/133602 for mac
   // http://crbug.com/140866 for linux
 
-#if defined(OS_WIN) || defined(OS_MACOSX)
+#if defined(OS_WIN)
     // Enable threaded compositing on Windows.
   threaded_compositing_probability = kDivisor;
+#elif defined(OS_MACOSX)
+  chrome::VersionInfo::Channel channel = chrome::VersionInfo::GetChannel();
+  if (channel == chrome::VersionInfo::CHANNEL_CANARY ||
+      channel == chrome::VersionInfo::CHANNEL_DEV) {
+    // Enable force-compositing-mode on the Mac.
+    force_compositing_mode_probability = kDivisor;
+  }
 #endif
 
   int force_compositing_group = trial->AppendGroup(
       content::kGpuCompositingFieldTrialForceCompositingEnabledName,
       force_compositing_mode_probability);
   int thread_group = trial->AppendGroup(
       content::kGpuCompositingFieldTrialThreadEnabledName,
       threaded_compositing_probability);
 
   bool force_compositing = (trial->group() == force_compositing_group);
   bool thread = (trial->group() == thread_group);
   UMA_HISTOGRAM_BOOLEAN("GPU.InForceCompositingModeFieldTrial",
                         force_compositing);
   UMA_HISTOGRAM_BOOLEAN("GPU.InCompositorThreadFieldTrial", thread);
 }
 
 }  // namespace gpu_util;