Remove unused paintScrollbarThumb impl.

content/shell/renderer/test_runner/mock_web_theme_engine.cc

 // 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.
 
 #include "content/shell/renderer/test_runner/mock_web_theme_engine.h"
 
+#if !defined(OS_MACOSX)
+
 #include "base/logging.h"
 #include "skia/ext/platform_canvas.h"
 #include "third_party/WebKit/public/platform/WebRect.h"
 #include "third_party/WebKit/public/platform/WebSize.h"
 #include "third_party/skia/include/core/SkRect.h"
 
 using blink::WebCanvas;
 using blink::WebColor;
 using blink::WebRect;
 using blink::WebThemeEngine;
@@ skipping 618 matching lines @@
         break;
     }
     default:
         // FIXME: Should we do something here to indicate that we got an invalid part?
         // Unfortunately, we can't assert because we don't have access to WTF or base.
         break;
     }
 }
 
 }  // namespace content
+
+#endif  // !defined(OS_MACOSX)