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

cc/trees/proxy_impl.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_IMPL_H_
 #define CC_TREES_PROXY_IMPL_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 34 matching lines @@
       CommitEarlyOutReason reason,
       base::TimeTicks main_thread_start_time,
       std::vector<std::unique_ptr<SwapPromise>> swap_promises);
   void SetVisibleOnImpl(bool visible);
   void ReleaseCompositorFrameSinkOnImpl(CompletionEvent* completion);
   void FinishGLOnImpl(CompletionEvent* completion);
   void NotifyReadyToCommitOnImpl(CompletionEvent* completion,
                                  LayerTreeHost* layer_tree_host,
                                  base::TimeTicks main_thread_start_time,
                                  bool hold_commit_for_activation);
+  void ResetTrees();
 
   void MainFrameWillHappenOnImplForTesting(CompletionEvent* completion,
                                            bool* main_frame_will_happen);
 
  private:
   // The members of this struct should be accessed on the impl thread only when
   // the main thread is blocked for a commit.
   struct BlockedMainCommitOnly {
     BlockedMainCommitOnly();
     ~BlockedMainCommitOnly();
@@ skipping 79 matching lines @@
 
   // Used to post tasks to ProxyMain on the main thread.
   base::WeakPtr<ProxyMain> proxy_main_weak_ptr_;
 
   DISALLOW_COPY_AND_ASSIGN(ProxyImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROXY_IMPL_H_