Make surface GetFormat pure virtual, add missing overrides.

ui/gl/gl_surface_wgl.cc

Index: ui/gl/gl_surface_wgl.cc
diff --git a/ui/gl/gl_surface_wgl.cc b/ui/gl/gl_surface_wgl.cc
index a971b152210c659c6caf45d25f8e7bfa72d83104..eb48cc462e451cdcda66723aa86ec1077dfaee97 100644
--- a/ui/gl/gl_surface_wgl.cc
+++ b/ui/gl/gl_surface_wgl.cc
@@ -320,6 +320,10 @@ void* NativeViewGLSurfaceWGL::GetHandle() {
   return device_context_;
 }
 
+GLSurfaceFormat NativeViewGLSurfaceWGL::GetFormat() {
+  return GLSurfaceFormat();
+}
+
 PbufferGLSurfaceWGL::PbufferGLSurfaceWGL(const gfx::Size& size)
     : size_(size),
       device_context_(NULL),
@@ -394,4 +398,8 @@ void* PbufferGLSurfaceWGL::GetHandle() {
   return device_context_;
 }
 
+GLSurfaceFormat PbufferGLSurfaceWGL::GetFormat() {
+  return GLSurfaceFormat();
+}
+
 }  // namespace gl