Plumb through EGL_NV_post_sub_buffer and GLX_MESA_copy_sub_buffer.

ui/gfx/gl/gl_surface.cc

Index: ui/gfx/gl/gl_surface.cc
diff --git a/ui/gfx/gl/gl_surface.cc b/ui/gfx/gl/gl_surface.cc
index 34d44641adc6c4e5094a26ab5f82fa24e2611ddb..78cada4d7678f9952a5a3c3cd8c9defd5216845c 100644
--- a/ui/gfx/gl/gl_surface.cc
+++ b/ui/gfx/gl/gl_surface.cc
@@ -94,6 +94,14 @@ unsigned int GLSurface::GetBackingFrameBufferObject() {
   return 0;
 }
 
+bool GLSurface::SupportsPostSubBuffer() {
+  return false;
+}
+
+bool GLSurface::PostSubBuffer(int x, int y, int width, int height) {
+  return false;
+}
+
 bool GLSurface::OnMakeCurrent(GLContext* context) {
   return true;
 }