cc: Invalidate framebuffer contents when clearing

cc/output/context_provider.h

 // Copyright (c) 2013 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_OUTPUT_CONTEXT_PROVIDER_H_
 #define CC_OUTPUT_CONTEXT_PROVIDER_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "cc/base/cc_export.h"
@@ skipping 24 matching lines @@
     bool map_image;
     bool map_sub;
     bool post_sub_buffer;
     bool set_visibility;
     bool shallow_flush;
     bool swapbuffers_complete_callback;
     bool texture_format_bgra8888;
     bool texture_rectangle;
     bool texture_storage;
     bool texture_usage;
+    bool discard_framebuffer;
 
     CC_EXPORT Capabilities();
   };
   // Returns the capabilities of the currently bound 3d context.
   virtual Capabilities ContextCapabilities() = 0;
 
   // Ask the provider to check if the contexts are valid or lost. If they are,
   // this should invalidate the provider so that it can be replaced with a new
   // one.
   virtual void VerifyContexts() = 0;
@@ skipping 25 matching lines @@
       const MemoryPolicyChangedCallback& memory_policy_changed_callback) = 0;
 
  protected:
   friend class base::RefCountedThreadSafe<ContextProvider>;
   virtual ~ContextProvider() {}
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_CONTEXT_PROVIDER_H_