Make surface GetFormat pure virtual, add missing overrides.

gpu/ipc/service/image_transport_surface_overlay_mac.mm

 // Copyright 2015 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 "gpu/ipc/service/image_transport_surface_overlay_mac.h"
 
 #include <CoreGraphics/CoreGraphics.h>
 #include <IOSurface/IOSurface.h>
 #include <OpenGL/CGLRenderers.h>
 #include <OpenGL/CGLTypes.h>
@@ skipping 286 matching lines @@
 }
 
 gfx::Size ImageTransportSurfaceOverlayMac::GetSize() {
   return gfx::Size();
 }
 
 void* ImageTransportSurfaceOverlayMac::GetHandle() {
   return nullptr;
 }
 
+gl::GLSurfaceFormat ImageTransportSurfaceOverlayMac::GetFormat() {
+  return gl::GLSurfaceFormat();
+}
+
 bool ImageTransportSurfaceOverlayMac::OnMakeCurrent(gl::GLContext* context) {
   // Ensure that the context is on the appropriate GL renderer. The GL renderer
   // will generally only change when the GPU changes.
   if (gl_renderer_id_ && context)
     context->share_group()->SetRendererID(gl_renderer_id_);
   return true;
 }
 
 bool ImageTransportSurfaceOverlayMac::ScheduleOverlayPlane(
     int z_order,
@@ skipping 67 matching lines @@
   gl_renderer_id_ = context_renderer_id & kCGLRendererIDMatchingMask;
 
   // Post a task holding a reference to the new GL context. The reason for
   // this is to avoid creating-then-destroying the context for every image
   // transport surface that is observing the GPU switch.
   base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE, base::Bind(&IOSurfaceContextNoOp, context_on_new_gpu));
 }
 
 }  // namespace gpu