Make surface GetFormat pure virtual, add missing overrides.

ui/gl/gl_surface.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_SURFACE_H_
 #define UI_GL_GL_SURFACE_H_
 
 #include <string>
 
 #include "base/callback.h"
@@ skipping 139 matching lines @@
   // available.
   virtual void* GetDisplay();
 
   // Get the platfrom specific configuration for this surface, if available.
   virtual void* GetConfig();
 
   // Get the key corresponding to the set of GLSurfaces that can be made current
   // with this GLSurface.
   virtual unsigned long GetCompatibilityKey();
 
-  // Get the GL pixel format of the surface, if available.
-  virtual GLSurfaceFormat GetFormat();
+  // Get the GL pixel format of the surface. Must be implemented in a
+  // subclass, though it's ok to just "return GLSurfaceFormat()" if
+  // the default is appropriate.
+  virtual GLSurfaceFormat GetFormat() = 0;
 
   // Get access to a helper providing time of recent refresh and period
   // of screen refresh. If unavailable, returns NULL.
   virtual gfx::VSyncProvider* GetVSyncProvider();
 
   // Schedule an overlay plane to be shown at swap time, or on the next
   // CommitOverlayPlanes call.
   // |z_order| specifies the stacking order of the plane relative to the
   // main framebuffer located at index 0. For the case where there is no
   // main framebuffer, overlays may be scheduled at 0, taking its place.
@@ skipping 119 matching lines @@
 // initialization fails.
 GL_EXPORT scoped_refptr<GLSurface> InitializeGLSurface(
     scoped_refptr<GLSurface> surface);
 
 GL_EXPORT scoped_refptr<GLSurface> InitializeGLSurfaceWithFormat(
     scoped_refptr<GLSurface> surface, GLSurfaceFormat format);
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_SURFACE_H_