Remove unused paintScrollbarThumb impl.

content/shell/renderer/test_runner/mock_web_theme_engine.h

 // Copyright 2014 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 CONTENT_SHELL_RENDERER_TEST_RUNNER_MOCK_WEB_THEME_ENGINE_H_
 #define CONTENT_SHELL_RENDERER_TEST_RUNNER_MOCK_WEB_THEME_ENGINE_H_
 
 #include "third_party/WebKit/public/platform/WebThemeEngine.h"
 
 namespace content {
 
 class MockWebThemeEngine : public blink::WebThemeEngine {
  public:
   virtual ~MockWebThemeEngine() {}
 
+#if !defined(OS_MACOSX)
   // blink::WebThemeEngine:
   virtual blink::WebSize getSize(blink::WebThemeEngine::Part);
   virtual void paint(blink::WebCanvas*,
                      blink::WebThemeEngine::Part,
                      blink::WebThemeEngine::State,
                      const blink::WebRect&,
                      const blink::WebThemeEngine::ExtraParams*);
+#endif  // !defined(OS_MACOSX)
 };
 
 }  // namespace content
 
 #endif  // CONTENT_SHELL_RENDERER_TEST_RUNNER_MOCK_WEB_THEME_ENGINE_H_