Make surface GetFormat pure virtual, add missing overrides.

gpu/ipc/service/image_transport_surface_overlay_mac.h

 // 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.
 
 #ifndef GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_OVERLAY_MAC_H_
 #define GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_OVERLAY_MAC_H_
 
 #include <list>
 #include <memory>
 #include <vector>
@@ skipping 32 matching lines @@
   void Destroy() override;
   bool Resize(const gfx::Size& size,
               float scale_factor,
               bool has_alpha) override;
   bool IsOffscreen() override;
   gfx::SwapResult SwapBuffers() override;
   gfx::SwapResult PostSubBuffer(int x, int y, int width, int height) override;
   bool SupportsPostSubBuffer() override;
   gfx::Size GetSize() override;
   void* GetHandle() override;
+  gl::GLSurfaceFormat GetFormat() override;
   bool OnMakeCurrent(gl::GLContext* context) override;
   bool ScheduleOverlayPlane(int z_order,
                             gfx::OverlayTransform transform,
                             gl::GLImage* image,
                             const gfx::Rect& bounds_rect,
                             const gfx::RectF& crop_rect) override;
   bool ScheduleCALayer(const ui::CARendererLayerParams& params) override;
   void ScheduleCALayerInUseQuery(
       std::vector<CALayerInUseQuery> queries) override;
   bool IsSurfaceless() const override;
@@ skipping 34 matching lines @@
   base::ScopedTypeRef<CGLContextObj> fence_context_obj_;
 
   // The renderer ID that all contexts made current to this surface should be
   // targeting.
   GLint gl_renderer_id_;
 };
 
 }  // namespace gpu
 
 #endif  // GPU_IPC_SERVICE_IMAGE_TRANSPORT_SURFACE_OVERLAY_MAC_H_