Allow GLSurface to indicate that it supports a specific extension.

ui/gfx/gl/gl_surface.h

Index: ui/gfx/gl/gl_surface.h
diff --git a/ui/gfx/gl/gl_surface.h b/ui/gfx/gl/gl_surface.h
index 95a346687335bf7fb2b14785c8981f3552c83f55..831836872d89727d12bb3084e41b9918ccd1371d 100644
--- a/ui/gfx/gl/gl_surface.h
+++ b/ui/gfx/gl/gl_surface.h
@@ -46,12 +46,15 @@ class GL_EXPORT GLSurface : public base::RefCounted<GLSurface> {
   // Get the underlying platform specific surface "handle".
   virtual void* GetHandle() = 0;
 
+  // Returns space separated list of surface specific extensions.
+  // The surface must be current.
+  virtual std::string GetExtensions();
+
   // Returns the internal frame buffer object name if the surface is backed by
   // FBO. Otherwise returns 0.
   virtual unsigned int GetBackingFrameBufferObject();
 
   // Copy part of the backbuffer to the frontbuffer.
-  virtual bool SupportsPostSubBuffer();
   virtual bool PostSubBuffer(int x, int y, int width, int height);
 
   static bool InitializeOneOff();