gpu: Bind dummy GL API when no context is current

ui/gl/gl_context.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_CONTEXT_H_
 #define UI_GL_GL_CONTEXT_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 99 matching lines @@
 
   // Returns the GL version string. The context must be current.
   virtual std::string GetGLVersion();
 
   // Returns the GL renderer string. The context must be current.
   virtual std::string GetGLRenderer();
 
  protected:
   virtual ~GLContext();
 
+  // Will release the current context when going out of scope, unless canceled.
+  class ScopedReleaseCurrent {
+   public:
+    ScopedReleaseCurrent();
+    ~ScopedReleaseCurrent();
+
+    void Cancel();
+
+   private:
+    bool canceled_;
+  };
+
   // Sets the GL api to the real hardware API (vs the VirtualAPI)
   static void SetRealGLApi();
   virtual void SetCurrent(GLSurface* surface);
 
   // Initialize function pointers to functions where the bound version depends
   // on GL version or supported extensions. Should be called immediately after
   // this context is made current.
   bool InitializeDynamicBindings();
 
   // Returns the last real (non-virtual) GLContext made current.
@@ skipping 22 matching lines @@
 
   virtual void SetCurrent(GLSurface* surface) OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(GLContextReal);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GL_GL_CONTEXT_H_