Make field trials activated in the GPU process be reflected in browser.

content/public/gpu/content_gpu_client.h

Index: content/public/gpu/content_gpu_client.h
diff --git a/content/public/gpu/content_gpu_client.h b/content/public/gpu/content_gpu_client.h
index 3704141283b580a11fb39f64c1079413f0285772..2c1f596199685d0e02820131b52039d37806ca81 100644
--- a/content/public/gpu/content_gpu_client.h
+++ b/content/public/gpu/content_gpu_client.h
@@ -5,6 +5,7 @@
 #ifndef CONTENT_PUBLIC_GPU_CONTENT_GPU_CLIENT_H_
 #define CONTENT_PUBLIC_GPU_CONTENT_GPU_CLIENT_H_
 
+#include "base/metrics/field_trial.h"
 #include "content/public/common/content_client.h"
 
 namespace gpu {
@@ -20,6 +21,11 @@ class CONTENT_EXPORT ContentGpuClient {
  public:
   virtual ~ContentGpuClient() {}
 
+  // Initializes the client. This sets up the field trial synchronization
+  // mechanism, which will notify |observer| when a field trial is activated,
+  // which should be used to inform the browser process of this state.
+  virtual void Initialize(base::FieldTrialList::Observer* observer) {}
+
   // Allows client to register Mojo services in |registry| on the GPU process.
   // The registered services will be exposed to the browser process through
   // GpuProcessHost.