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

cc/trees/single_thread_proxy.h

 // 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.
 
 #ifndef CC_TREES_SINGLE_THREAD_PROXY_H_
 #define CC_TREES_SINGLE_THREAD_PROXY_H_
 
 #include <limits>
 
 #include "base/cancelable_callback.h"
@@ skipping 40 matching lines @@
   bool CommitRequested() const override;
   void MainThreadHasStoppedFlinging() override {}
   void Start() override;
   void Stop() override;
   void SetMutator(std::unique_ptr<LayerTreeMutator> mutator) override;
   bool SupportsImplScrolling() const override;
   bool MainFrameWillHappenForTesting() override;
   void UpdateBrowserControlsState(BrowserControlsState constraints,
                                   BrowserControlsState current,
                                   bool animate) override;
+  void ResetTrees() override {}
 
   // SchedulerClient implementation
   void WillBeginImplFrame(const BeginFrameArgs& args) override;
   void DidFinishImplFrame() override;
   void ScheduledActionSendBeginMainFrame(const BeginFrameArgs& args) override;
   DrawResult ScheduledActionDrawIfPossible() override;
   DrawResult ScheduledActionDrawForced() override;
   void ScheduledActionCommit() override;
   void ScheduledActionActivateSyncTree() override;
   void ScheduledActionBeginCompositorFrameSinkCreation() override;
@@ skipping 160 matching lines @@
  private:
   DebugScopedSetImplThread impl_thread_;
   DebugScopedSetMainThreadBlocked main_thread_blocked_;
 
   DISALLOW_COPY_AND_ASSIGN(DebugScopedSetImplThreadAndMainThreadBlocked);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_SINGLE_THREAD_PROXY_H_