MacViews: Implement scrollbar theming.

ui/native_theme/native_theme_base.cc

 // Copyright (c) 2012 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/native_theme/native_theme_base.h"
 
 #include <limits>
 
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 218 matching lines @@
     case kPushButton:
       PaintButton(canvas, state, rect, extra.button);
       break;
     case kRadio:
       PaintRadio(canvas, state, rect, extra.button);
       break;
     case kScrollbarDownArrow:
     case kScrollbarUpArrow:
     case kScrollbarLeftArrow:
     case kScrollbarRightArrow:
-      PaintArrowButton(canvas, rect, part, state);
+      if (scrollbar_button_length_ > 0)
+        PaintArrowButton(canvas, rect, part, state);
       break;
     case kScrollbarHorizontalThumb:
     case kScrollbarVerticalThumb:
       PaintScrollbarThumb(canvas, part, state, rect);
       break;
     case kScrollbarHorizontalTrack:
     case kScrollbarVerticalTrack:
       PaintScrollbarTrack(canvas, part, state, extra.scrollbar_track, rect);
       break;
     case kScrollbarHorizontalGripper:
@@ skipping 835 matching lines @@
   SkScalar min_diff = Clamp((hsv1[1] + hsv2[1]) * 1.2f, 0.28f, 0.5f);
   SkScalar diff = Clamp(fabs(hsv1[2] - hsv2[2]) / 2, min_diff, 0.5f);
 
   if (hsv1[2] + hsv2[2] > 1.0)
     diff = -diff;
 
   return SaturateAndBrighten(hsv2, -0.2f, diff);
 }
 
 }  // namespace ui