Add an Invalidate method to GLFence.

ui/gl/gl_fence.h

 // Copyright (c) 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 UI_GL_GL_FENCE_H_
 #define UI_GL_GL_FENCE_H_
 
 #include "base/macros.h"
 #include "ui/gl/gl_export.h"
 
@@ skipping 13 matching lines @@
   // Will block the server if supported, but might fall back to blocking the
   // client.
   virtual void ServerWait() = 0;
 
   // Returns true if re-setting state is supported.
   virtual bool ResetSupported();
 
   // Resets the fence to the original state.
   virtual void ResetState();
 
+  // Loses the reference to the fence. Useful if the context is lost.
+  virtual void Invalidate();
+
  private:
   DISALLOW_COPY_AND_ASSIGN(GLFence);
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_FENCE_H_