Make surface GetFormat pure virtual, add missing overrides.

android_webview/browser/aw_gl_surface.cc

 // Copyright 2013 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.
 
 #include "android_webview/browser/aw_gl_surface.h"
 
 #include "android_webview/browser/scoped_app_gl_state_restore.h"
 
 namespace android_webview {
 
@@ skipping 21 matching lines @@
 }
 
 void* AwGLSurface::GetHandle() {
   return NULL;
 }
 
 void* AwGLSurface::GetDisplay() {
   return NULL;
 }
 
+GLSurfaceFormat AwGLSurface::GetFormat() {
+  return GLSurfaceFormat();

[boliu, 2017/02/23 21:33:31]

add NOTIMPLEMENTED here?

[klausw, 2017/02/23 22:08:47]

No, this is the complete implementation already. Requiring the overrides makes
it explicit that there's no need to distinguish implementation-dependent format
properties.

I've added comments to gl_surface_format.h to make the intended semantics a bit
clearer.

+}
+
 }  // namespace android_webview