Aura overlay scrollbars adjust color for dark backgrounds

ui/native_theme/native_theme_aura.h

 // 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.
 
 #ifndef UI_NATIVE_THEME_NATIVE_THEME_AURA_H_
 #define UI_NATIVE_THEME_NATIVE_THEME_AURA_H_
 
 #include "base/macros.h"
 #include "ui/native_theme/native_theme_base.h"
 
@@ skipping 24 matching lines @@
                         Part direction,
                         State state) const override;
   void PaintScrollbarTrack(SkCanvas* canvas,
                            Part part,
                            State state,
                            const ScrollbarTrackExtraParams& extra_params,
                            const gfx::Rect& rect) const override;
   void PaintScrollbarThumb(SkCanvas* canvas,
                            Part part,
                            State state,
-                           const gfx::Rect& rect) const override;
+                           const gfx::Rect& rect,
+                           ScrollbarOverlayColorTheme theme) const override;
   void PaintScrollbarCorner(SkCanvas* canvas,
                             State state,
                             const gfx::Rect& rect) const override;
 
-  void PaintScrollbarThumbStateTransition(SkCanvas* canvas,
-                                          Part part,
-                                          State startState,
-                                          State endState,
-                                          double progress,
-                                          const gfx::Rect& rect) const override;
+  void PaintScrollbarThumbStateTransition(

[bokan, 2016/10/27 15:14:49]

The only actual caller of this method is PaintScrollbarThumb. Remove this method
and put its implementation directly in PaintScrollbarThumb. Also remove
NativeThemeBase::PaintScrollbarThumbTransition which calls here but has no
callers.

+      SkCanvas* canvas,
+      Part part,
+      State startState,
+      State endState,
+      double progress,
+      const gfx::Rect& rect,
+      ScrollbarOverlayColorTheme theme) const override;
   gfx::Size GetPartSize(Part part,
                         State state,
                         const ExtraParams& extra) const override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NativeThemeAura);
 };
 
 }  // namespace ui
 
 #endif  // UI_NATIVE_THEME_NATIVE_THEME_AURA_H_