Add optimization for CHROMIUM_subscribe_uniform extension.

gpu/command_buffer/service/context_group.cc

Index: gpu/command_buffer/service/context_group.cc
diff --git a/gpu/command_buffer/service/context_group.cc b/gpu/command_buffer/service/context_group.cc
index 0206d88f13a47dad8147b9f9acb772e87de53232..3caec4197fcaa365f943b8907499188c1fc72abe 100644
--- a/gpu/command_buffer/service/context_group.cc
+++ b/gpu/command_buffer/service/context_group.cc
@@ -32,11 +32,13 @@ ContextGroup::ContextGroup(
     const scoped_refptr<MemoryTracker>& memory_tracker,
     const scoped_refptr<ShaderTranslatorCache>& shader_translator_cache,
     const scoped_refptr<FeatureInfo>& feature_info,
+    const scoped_refptr<SubscriptionRefSet>& subscription_ref_set,
     const scoped_refptr<ValueStateMap>& pending_valuebuffer_state,
     bool bind_generates_resource)
     : mailbox_manager_(mailbox_manager),
       memory_tracker_(memory_tracker),
       shader_translator_cache_(shader_translator_cache),
+      subscription_ref_set_(subscription_ref_set),
       pending_valuebuffer_state_(pending_valuebuffer_state),
       enforce_gl_minimums_(CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kEnforceGLMinimums)),
@@ -56,6 +58,8 @@ ContextGroup::ContextGroup(
   {
     if (!mailbox_manager_.get())
       mailbox_manager_ = new MailboxManagerImpl;
+    if (!subscription_ref_set_.get())
+      subscription_ref_set_ = new SubscriptionRefSet();
     if (!pending_valuebuffer_state_.get())
       pending_valuebuffer_state_ = new ValueStateMap();
     if (!feature_info.get())
@@ -128,7 +132,8 @@ bool ContextGroup::Initialize(
       depth24_supported));
   shader_manager_.reset(new ShaderManager());
   valuebuffer_manager_.reset(
-      new ValuebufferManager(pending_valuebuffer_state_.get()));
+      new ValuebufferManager(subscription_ref_set_.get(),
+                             pending_valuebuffer_state_.get()));
 
   // Lookup GL things we need to know.
   const GLint kGLES2RequiredMinimumVertexAttribs = 8u;