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

cc/trees/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_PROXY_H_
 #define CC_TREES_PROXY_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 55 matching lines @@
   virtual void Stop() = 0;
 
   virtual void SetMutator(std::unique_ptr<LayerTreeMutator> mutator) = 0;
 
   virtual bool SupportsImplScrolling() const = 0;
 
   virtual void UpdateBrowserControlsState(BrowserControlsState constraints,
                                           BrowserControlsState current,
                                           bool animate) = 0;
 
+  virtual void ResetTrees() = 0;
+
   // Testing hooks
   virtual bool MainFrameWillHappenForTesting() = 0;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROXY_H_