Paint state transition for overlay 9 patch scrollbars

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 138 matching lines @@
     case kWindowResizeGripper:
       NOTIMPLEMENTED();
       break;
     default:
       NOTREACHED() << "Unknown theme part: " << part;
       break;
   }
   return gfx::Size();
 }
 
+void NativeThemeBase::PaintStateTransition(SkCanvas* canvas,
+                                           Part part,
+                                           State startState,
+                                           State endState,
+                                           double progress,
+                                           const gfx::Rect& rect) const {
+  if (rect.IsEmpty())
+    return;
+
+  // Currently state transition is animation only working for overlay scrollbars
+  // on Aura platforms.
+  switch (part) {
+    case kScrollbarHorizontalThumb:
+    case kScrollbarVerticalThumb:
+      PaintScrollbarThumbStateTransition(
+          canvas, startState, endState, progress, rect);
+      break;
+    default:
+      NOTREACHED() << "Does not support state transition for this part:"
+                   << part;
+      break;
+  }
+  return;
+}
+
 void NativeThemeBase::Paint(SkCanvas* canvas,
                             Part part,
                             State state,
                             const gfx::Rect& rect,
                             const ExtraParams& extra) const {
   if (rect.IsEmpty())
     return;
 
   switch (part) {
     // Please keep these in the order of NativeTheme::Part.
@@ skipping 893 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