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

chrome/browser/gpu_util.cc

Index: chrome/browser/gpu_util.cc
===================================================================
--- chrome/browser/gpu_util.cc	(revision 140632)
+++ chrome/browser/gpu_util.cc	(working copy)
@@ -7,6 +7,7 @@
 #include <vector>
 
 #include "base/command_line.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/string_number_conversions.h"
 #include "base/string_util.h"
@@ -14,6 +15,7 @@
 #include "base/sys_info.h"
 #include "base/values.h"
 #include "base/version.h"
+#include "chrome/browser/browser_trial.h"
 #include "chrome/browser/gpu_blacklist.h"
 #include "content/public/browser/gpu_data_manager.h"
 #include "content/public/common/content_switches.h"
@@ -203,6 +205,17 @@
   return JoinString(matches, ',');
 }
 
+bool InForceCompositingFieldTrial() {

[SteveT, 2012/06/06 13:06:02]

nit: Indent is 4 here instead of 2.

+    base::FieldTrial* trial =
+        base::FieldTrialList::Find(BrowserTrial::kForceCompositingModeTrial);
+    if (!trial)
+      return false;

[Ilya Sherman, 2012/06/06 09:50:21]

Can this be a DCHECK rather than an if-stmt?  (See comment below for
motivation.)

+    if (trial->group_name() != std::string("enable"))

[Ilya Sherman, 2012/06/06 09:50:21]

nit: return trial->group_name() == "enable";

+      return false;
+
+    return true;
+}
+
 Value* GetFeatureStatus() {
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
   bool gpu_access_blocked = !GpuDataManager::GetInstance()->GpuAccessAllowed();
@@ -314,8 +327,9 @@
             (!CommandLine::ForCurrentProcess()->HasSwitch(
                 switches::kDisableThreadedCompositing));
         if (kGpuFeatureInfo[i].name == "compositing" &&
-            CommandLine::ForCurrentProcess()->HasSwitch(
-                switches::kForceCompositingMode))
+            (CommandLine::ForCurrentProcess()->HasSwitch(
+                 switches::kForceCompositingMode) ||
+             InForceCompositingFieldTrial()))

[Ilya Sherman, 2012/06/06 09:50:21]

Will the field trial always be set up by the time this code is reached?  If not,
is it ok that this function might return different results depending on when it
is called?

           status += "_force";
         if (kGpuFeatureInfo[i].name == "compositing" &&
             has_thread)