Make surface GetFormat pure virtual, add missing overrides.

android_webview/browser/aw_gl_surface.cc

Index: android_webview/browser/aw_gl_surface.cc
diff --git a/android_webview/browser/aw_gl_surface.cc b/android_webview/browser/aw_gl_surface.cc
index c2ed5ab59eaef8895d4ef214edbdb36042ba14e6..8b4fd77a7bf6f174491bcbb744a79b430a501ca4 100644
--- a/android_webview/browser/aw_gl_surface.cc
+++ b/android_webview/browser/aw_gl_surface.cc
@@ -39,4 +39,8 @@ 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