Enable by default threaded compositing on windows and FCM on mac

content/common/compositor_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 "content/public/common/compositor_util.h"
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "content/public/common/content_constants.h"
 #include "content/public/common/content_switches.h"
 
 namespace content {
 
 bool IsThreadedCompositingEnabled() {
 #if defined(OS_WIN) && defined(USE_AURA)
   // We always want compositing on Aura Windows.
   return true;
 #endif
 
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
-  if (command_line.HasSwitch(switches::kEnableThreadedCompositing) &&
-      !command_line.HasSwitch(switches::kDisableThreadedCompositing))
+
+  // Command line switches take precedence over field trials.
+  if (command_line.HasSwitch(switches::kDisableForceCompositingMode) ||
+      command_line.HasSwitch(switches::kDisableThreadedCompositing))
+    return false;
+
+  if (command_line.HasSwitch(switches::kEnableThreadedCompositing))
     return true;
 
   base::FieldTrial* trial =
       base::FieldTrialList::Find(content::kGpuCompositingFieldTrialName);
   return trial &&
          trial->group_name() ==
              content::kGpuCompositingFieldTrialThreadEnabledName;
 }
 
 bool IsForceCompositingModeEnabled() {
 #if defined(OS_WIN) && defined(USE_AURA)
   // We always want compositing on Aura Windows.
   return true;
 #endif
 
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
-  if (command_line.HasSwitch(switches::kForceCompositingMode) &&
-      !command_line.HasSwitch(switches::kDisableForceCompositingMode))
+
+  // Command line switches take precedence over field trials.
+  if (command_line.HasSwitch(switches::kDisableForceCompositingMode))
+    return false;
+
+  if (command_line.HasSwitch(switches::kForceCompositingMode))
     return true;
 
   base::FieldTrial* trial =
       base::FieldTrialList::Find(content::kGpuCompositingFieldTrialName);
 
   // Force compositing is enabled in both the force compositing
   // and threaded compositing mode field trials.
   return trial &&
         (trial->group_name() ==
             content::kGpuCompositingFieldTrialForceCompositingEnabledName ||
          trial->group_name() ==
             content::kGpuCompositingFieldTrialThreadEnabledName);
 }
 
 }  // compositor_util