cc: Make OutputSurface::BindToClient pure virtual and not return bool

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 <stddef.h>
 #include <stdint.h>
 
@@ skipping 56 matching lines @@
   // Invalidates the cached OpenGL state in GrContext.
   // See skia GrContext::resetContext for details.
   virtual void InvalidateGrContext(uint32_t state) = 0;
 
   // Returns the capabilities of the currently bound 3d context.
   virtual gpu::Capabilities ContextCapabilities() = 0;
 
   // Sets a callback to be called when the context is lost. This should be
   // called from the same thread that the context is bound to. To avoid races,
   // it should be called before BindToCurrentThread().
+  // Implementation note: Implementations must avoid post-tasking the provided
+  // |lost_context_callback| directly as clients expect the method to not be
+  // called once they call SetLostContextCallback() again with a different
+  // callback.
   typedef base::Closure LostContextCallback;
   virtual void SetLostContextCallback(
       const LostContextCallback& lost_context_callback) = 0;
 
   // Below are helper methods for ScopedContextLock. Use that instead of calling
   // these directly.
   //
   // Detaches debugging thread checkers to allow use of the provider from the
   // current thread. This can be called on any thread.
   virtual void DetachFromThread() {}
   // Returns the lock that should be held if using this context from multiple
   // threads. This can be called on any thread.
   virtual base::Lock* GetLock() = 0;
 
  protected:
   friend class base::RefCountedThreadSafe<ContextProvider>;
   virtual ~ContextProvider() {}
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_CONTEXT_PROVIDER_H_