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

chrome/browser/gpu_util.h

Index: chrome/browser/gpu_util.h
===================================================================
--- chrome/browser/gpu_util.h	(revision 140632)
+++ chrome/browser/gpu_util.h	(working copy)
@@ -69,6 +69,13 @@
 // Send UMA histograms about the enabled features.
 void UpdateStats();
 
+// Returs whether this client has been selected for the force-compositing-mode
+// trial.
+bool InForceCompositingModeTrial();
+
+// Sets up the force-compositing-mode field trial.
+void InitializeForceCompositingModeFieldTrial();
+
 }  // namespace gpu_util
 
 #endif  // CHROME_BROWSER_GPU_UTIL_H_