Add field trial for enabling Stage3D in XP

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 c3cd7f5430487d599bf622e06fda70fb6f788882..b4221eca6e88addc629eef7120cd5ce02686f87c 100644
--- a/chrome/browser/chrome_gpu_util.cc
+++ b/chrome/browser/chrome_gpu_util.cc
@@ -21,6 +21,43 @@ using content::GpuDataManager;
 
 namespace gpu_util {
 
+bool ShouldRunStage3DFieldTrial() {
+#if !defined(OS_WIN)
+  return false;
+#else
+  if (base::win::GetVersion() >= base::win::VERSION_VISTA)
+    return false;
+  return true;
+#endif
+}
+
+void InitializeStage3DFieldTrial() {
+  if (!ShouldRunStage3DFieldTrial()) {
+    base::FieldTrial* trial =
+        base::FieldTrialList::Find(content::kStage3DFieldTrialName);
+    if (trial)
+      trial->Disable();
+    return;
+  }
+
+  const base::FieldTrial::Probability kDivisor = 1000;
+  scoped_refptr<base::FieldTrial> trial(
+    base::FieldTrialList::FactoryGetFieldTrial(
+        content::kStage3DFieldTrialName, kDivisor,
+        content::kStage3DFieldTrialEnabledName, 2013, 3, 1, NULL));
+
+  // Produce the same result on every run of this client.
+  trial->UseOneTimeRandomization();
+
+  // Kill-switch, so disabled unless we get info from server.
+  int blacklisted_group = trial->AppendGroup(
+      content::kStage3DFieldTrialBlacklistedName, kDivisor);
+
+  bool enabled = (trial->group() != blacklisted_group);
+
+  UMA_HISTOGRAM_BOOLEAN("GPU.Stage3DFieldTrial", enabled);
+}
+
 void DisableCompositingFieldTrial() {
   base::FieldTrial* trial =
       base::FieldTrialList::Find(content::kGpuCompositingFieldTrialName);