Revert 196933 "Turn on threaded compositing in OS X for continuo..."

trunk/src/chrome/browser/gpu/chrome_gpu_util.cc

Index: trunk/src/chrome/browser/gpu/chrome_gpu_util.cc
===================================================================
--- trunk/src/chrome/browser/gpu/chrome_gpu_util.cc	(revision 196963)
+++ trunk/src/chrome/browser/gpu/chrome_gpu_util.cc	(working copy)
@@ -112,9 +112,16 @@
   // http://crbug.com/133602 for mac
   // http://crbug.com/140866 for linux
 
-#if defined(OS_WIN) || defined(OS_MACOSX)
-  // Enable threaded compositing on Windows and Mac.
+#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(