Make surface GetFormat pure virtual, add missing overrides.

ui/gl/init/gl_factory_mac.cc

 // Copyright 2016 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 "ui/gl/init/gl_factory.h"
 
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/gl/gl_bindings.h"
@@ skipping 25 matching lines @@
   void Destroy() override {}
   bool IsOffscreen() override { return true; }
   gfx::SwapResult SwapBuffers() override {
     NOTREACHED() << "Cannot call SwapBuffers on a NoOpGLSurface.";
     return gfx::SwapResult::SWAP_FAILED;
   }
   gfx::Size GetSize() override { return size_; }
   void* GetHandle() override { return nullptr; }
   void* GetDisplay() override { return nullptr; }
   bool IsSurfaceless() const override { return true; }
+  GLSurfaceFormat GetFormat() override { return GLSurfaceFormat(); }
 
  protected:
   ~NoOpGLSurface() override {}
 
  private:
   gfx::Size size_;
 
   DISALLOW_COPY_AND_ASSIGN(NoOpGLSurface);
 };
 
@@ skipping 81 matching lines @@
     case kGLImplementationStubGL:
       return new GLSurfaceStub;
     default:
       NOTREACHED();
       return nullptr;
   }
 }
 
 }  // namespace init
 }  // namespace gl