Adding a field trial for testing --force-compositing-mode on 50% of

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
===================================================================
--- chrome/browser/chrome_browser_main.cc	(revision 140632)
+++ chrome/browser/chrome_browser_main.cc	(working copy)
@@ -160,6 +160,7 @@
 #if defined(OS_MACOSX)
 #include <Security/Security.h>
 
+#include "base/mac/mac_util.h"
 #include "base/mac/scoped_nsautorelease_pool.h"
 #include "chrome/browser/mac/keystone_glue.h"
 #endif
@@ -519,6 +520,7 @@
 // static
 bool ChromeBrowserMainParts::disable_enforcing_cookie_policies_for_tests_ =
     false;
+bool ChromeBrowserMainParts::in_force_compositing_mode_trial_ = false;
 
 ChromeBrowserMainParts::ChromeBrowserMainParts(
     const content::MainFunctionParams& parameters)
@@ -1011,6 +1013,41 @@
   }
 }
 
+void ChromeBrowserMainParts::ForceCompositingModeFieldTrial() {
+// Enable the field trial only on the desktop OS's.
+#if !(defined(OS_WIN) || defined(OS_MACOSX) || defined(OS_LINUX))
+  return;
+#endif
+  chrome::VersionInfo::Channel channel = chrome::VersionInfo::GetChannel();
+  // Only run the trial on the Canary channel.
+  if (channel != chrome::VersionInfo::CHANNEL_CANARY)
+    return;
+#if defined(OS_WIN)
+  // Don't run the trial on windows XP.

[Ilya Sherman, 2012/06/06 22:31:51]

nit: "windows" -> "Windows"

[vangelis, 2012/06/06 23:44:44]

Done.

+  if (base::win::GetVersion() < base::win::VERSION_VISTA)
+    return;
+#elif defined(OS_MACOSX)
+  // Accelerated compositing is only implemented on Mac OSX 10.6 or later.
+  if (base::mac::IsOSLeopardOrEarlier())
+    return;
+#endif
+
+  const base::FieldTrial::Probability kDivisor = 100;
+  scoped_refptr<base::FieldTrial> trial(
+    base::FieldTrialList::FactoryGetFieldTrial(
+        "ForceCompositingMode", kDivisor, "disable", 2012, 12, 31, NULL));
+
+  // Produce the same result on every run of this client.
+  trial->UseOneTimeRandomization();
+  // 50% probability of being in the enabled group.
+  const base::FieldTrial::Probability kEnableProbability = 50;
+  int enable_group = trial->AppendGroup("enable", kEnableProbability);
+
+  in_force_compositing_mode_trial_ = (trial->group() == enable_group);
+  UMA_HISTOGRAM_BOOLEAN("GPU.InForceCompositingModeFieldTrial",
+                        in_force_compositing_mode_trial_);
+}
+
 void ChromeBrowserMainParts::DomainBoundCertsFieldTrial() {
   chrome::VersionInfo::Channel channel = chrome::VersionInfo::GetChannel();
   if (channel == chrome::VersionInfo::CHANNEL_CANARY) {
@@ -1102,6 +1139,7 @@
   DefaultAppsFieldTrial();
   AutoLaunchChromeFieldTrial();
   DomainBoundCertsFieldTrial();
+  ForceCompositingModeFieldTrial();
   SetupUniformityFieldTrials();
   AutocompleteFieldTrial::Activate();
 }