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

cc/test/fake_proxy.h

 // Copyright 2012 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_TEST_FAKE_PROXY_H_
 #define CC_TEST_FAKE_PROXY_H_
 
 #include "base/single_thread_task_runner.h"
 #include "cc/trees/layer_tree_host.h"
 #include "cc/trees/proxy.h"
@@ skipping 22 matching lines @@
   void MainThreadHasStoppedFlinging() override {}
   bool CommitRequested() const 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 {}
 
  private:
   LayerTreeHost* layer_tree_host_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_PROXY_H_