Clear renderer compositor trees if new page does not render in 4 seconds

cc/trees/proxy_main.h

 // Copyright 2015 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.
 
 #ifndef CC_TREES_PROXY_MAIN_H_
 #define CC_TREES_PROXY_MAIN_H_
 
 #include "base/macros.h"
 #include "cc/base/cc_export.h"
 #include "cc/input/browser_controls_state.h"
@@ skipping 68 matching lines @@
   void MainThreadHasStoppedFlinging() override;
   void Start() override;
   void Stop() override;
   bool SupportsImplScrolling() const override;
   void SetMutator(std::unique_ptr<LayerTreeMutator> mutator) override;
   bool MainFrameWillHappenForTesting() override;
   void ReleaseCompositorFrameSink() override;
   void UpdateBrowserControlsState(BrowserControlsState constraints,
                                   BrowserControlsState current,
                                   bool animate) override;
+  void ResetTrees() override;
 
   // Returns |true| if the request was actually sent, |false| if one was
   // already outstanding.
   bool SendCommitRequestToImplThreadIfNeeded(
       CommitPipelineStage required_stage);
   bool IsMainThread() const;
   bool IsImplThread() const;
   base::SingleThreadTaskRunner* ImplThreadTaskRunner();
 
   void InitializeOnImplThread(CompletionEvent* completion_event);
@@ skipping 31 matching lines @@
   std::unique_ptr<ProxyImpl> proxy_impl_;
 
   base::WeakPtrFactory<ProxyMain> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ProxyMain);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROXY_MAIN_H_