Enable by default threaded compositing on windows and FCM on mac

chrome/browser/chrome_gpu_util.cc

Index: chrome/browser/chrome_gpu_util.cc
diff --git a/chrome/browser/chrome_gpu_util.cc b/chrome/browser/chrome_gpu_util.cc
index b4221eca6e88addc629eef7120cd5ce02686f87c..048ed2d34530391cfc7cb27822e11431ff0f0a48 100644
--- a/chrome/browser/chrome_gpu_util.cc
+++ b/chrome/browser/chrome_gpu_util.cc
@@ -71,6 +71,12 @@ bool ShouldRunCompositingFieldTrial() {
   return false;
 #endif
 
+// Necessary for linux_chromeos build since it defines both OS_LINUX
+// and OS_CHROMEOS .
+#if defined(OS_CHROMEOS)
+  return false;
+#endif
+
 #if defined(OS_WIN)
   // Don't run the trial on Windows XP.
   if (base::win::GetVersion() < base::win::VERSION_VISTA)
@@ -106,42 +112,40 @@ void InitializeCompositingFieldTrial() {
   }
 
   const base::FieldTrial::Probability kDivisor = 3;
+  // Note: This field trial should be removed once we're comfortable with
+  // turning force compositing mode and threaded compositing on all relevant
+  // platforms (see crbug.com/149991).
   scoped_refptr<base::FieldTrial> trial(
     base::FieldTrialList::FactoryGetFieldTrial(
         content::kGpuCompositingFieldTrialName, kDivisor,
-        "disable", 2012, 12, 31, NULL));
+        "disable", 2013, 12, 31, NULL));
 
   // Produce the same result on every run of this client.
   trial->UseOneTimeRandomization();
 
+  // Note: The static field trial probabilities set here can be overwritten
+  // at runtime by Finch. Changing these static values won't have an effect
+  // if a Finch study is active.
   base::FieldTrial::Probability force_compositing_mode_probability = 0;
   base::FieldTrial::Probability threaded_compositing_probability = 0;
 
+  // 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)
+  // threaded-compositing turned on by default on Windows.
+  // (Windows XP is excluded explicitly in ShouldRunCompositingFieldTrial)
+  threaded_compositing_probability = 3;
+#elif defined(OS_LINUX) || defined(OS_MACOSX)
   chrome::VersionInfo::Channel channel = chrome::VersionInfo::GetChannel();
-  if (channel == chrome::VersionInfo::CHANNEL_STABLE ||
-      channel == chrome::VersionInfo::CHANNEL_BETA) {
-    // Stable and Beta channels: Non-threaded force-compositing-mode on by
-    // default (mac and windows only).
-#if defined(OS_WIN) || defined(OS_MACOSX)
-    force_compositing_mode_probability = 3;
-#endif
-  } else if (channel == chrome::VersionInfo::CHANNEL_DEV ||
-             channel == chrome::VersionInfo::CHANNEL_CANARY) {
-    // Dev and Canary channels: force-compositing-mode and
-    // threaded-compositing on with 1/3 probability each.
+  if (channel != chrome::VersionInfo::CHANNEL_STABLE &&
+      channel != chrome::VersionInfo::CHANNEL_BETA) {
+    // On channels < beta, force-compositing-mode on
+    // with 33% probability.
     force_compositing_mode_probability = 1;
-
-#if defined(OS_MACOSX) || defined(OS_LINUX)
-    // Threaded compositing mode isn't feature complete on mac or linux yet:
-    // http://crbug.com/133602 for mac
-    // http://crbug.com/140866 for linux
-    threaded_compositing_probability = 0;
-#else
-    if (!CommandLine::ForCurrentProcess()->HasSwitch(
-            switches::kDisableThreadedCompositing))
-        threaded_compositing_probability = 1;
-#endif
   }
+#endif
 
   int force_compositing_group = trial->AppendGroup(
       content::kGpuCompositingFieldTrialForceCompositingEnabledName,