Simplify rate limiting since it's main thread shared context only

cc/trees/layer_tree_host.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include <algorithm>
 #include <stack>
 #include <string>
 
@@ skipping 165 matching lines @@
 
   if (root_layer_.get())
     root_layer_->SetLayerTreeHost(NULL);
 
   if (proxy_) {
     DCHECK(proxy_->IsMainThread());
     proxy_->Stop();
   }
 
   s_num_layer_tree_instances--;
-  RateLimiterMap::iterator it = rate_limiters_.begin();
-  if (it != rate_limiters_.end())
-    it->second->Stop();
 
   if (root_layer_.get()) {
     // The layer tree must be destroyed before the layer tree host. We've
     // made a contract with our animation controllers that the registrar
     // will outlive them, and we must make good.
     root_layer_ = NULL;
   }
 }
 
 void LayerTreeHost::SetLayerTreeHostClientReady() {
@@ skipping 905 matching lines @@
     // value, then the layer can early out without needing a full commit.
     if (root_scroll_layer) {
       root_scroll_layer->SetScrollOffsetFromImplSide(
           root_scroll_layer->scroll_offset() + root_scroll_delta);
     }
     ApplyPageScaleDeltaFromImplSide(info.page_scale_delta);
     client_->ApplyScrollAndScale(root_scroll_delta, info.page_scale_delta);
   }
 }
 
-void LayerTreeHost::StartRateLimiter(WebKit::WebGraphicsContext3D* context3d) {
+void LayerTreeHost::StartRateLimiter() {
   if (animating_)
     return;
 
-  DCHECK(context3d);
-  RateLimiterMap::iterator it = rate_limiters_.find(context3d);
-  if (it != rate_limiters_.end()) {
-    it->second->Start();
-  } else {
-    scoped_refptr<RateLimiter> rate_limiter =
-        RateLimiter::Create(context3d, this, proxy_->MainThreadTaskRunner());
-    rate_limiters_[context3d] = rate_limiter;
-    rate_limiter->Start();
+  if (!rate_limit_timer_.IsRunning()) {
+    rate_limit_timer_.Start(FROM_HERE,
+                            base::TimeDelta(),
+                            this,
+                            &LayerTreeHost::RateLimit);
   }
 }
 
-void LayerTreeHost::StopRateLimiter(WebKit::WebGraphicsContext3D* context3d) {
-  RateLimiterMap::iterator it = rate_limiters_.find(context3d);
-  if (it != rate_limiters_.end()) {
-    it->second->Stop();
-    rate_limiters_.erase(it);
-  }
+void LayerTreeHost::StopRateLimiter() {
+  rate_limit_timer_.Stop();
 }
 
 void LayerTreeHost::RateLimit() {
   // Force a no-op command on the compositor context, so that any ratelimiting
   // commands will wait for the compositing context, and therefore for the
   // SwapBuffers.
   proxy_->ForceSerializeOnSwapBuffers();
+  client_->RateLimitSharedMainThreadContext();
 }
 
 bool LayerTreeHost::AlwaysUsePartialTextureUpdates() {
   if (!proxy_->GetRendererCapabilities().allow_partial_texture_updates)
     return false;
   return !proxy_->HasImplThread();
 }
 
 size_t LayerTreeHost::MaxPartialTextureUpdates() const {
   size_t max_partial_texture_updates = 0;
@@ skipping 131 matching lines @@
 
 bool LayerTreeHost::ScheduleMicroBenchmark(
     const std::string& benchmark_name,
     scoped_ptr<base::Value> value,
     const MicroBenchmark::DoneCallback& callback) {
   return micro_benchmark_controller_.ScheduleRun(
       benchmark_name, value.Pass(), callback);
 }
 
 }  // namespace cc