Change Aura overlay scrollbars from solid color to painted scrollbars.

third_party/WebKit/Source/platform/scroll/ScrollbarThemeAura.cpp

 /*
  * Copyright (c) 2008, 2009, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 112 matching lines @@
       state = WebThemeEngine::StateHover;
   }
 
   return PartPaintingParams(paintPart, state);
 }
 
 }  // namespace
 
 ScrollbarTheme& ScrollbarTheme::nativeTheme() {
   if (RuntimeEnabledFeatures::overlayScrollbarsEnabled()) {
+    int thickness = Platform::current()

[jbroman, 2016/10/18 20:39:26]

nit: this fetches the thickness every time, even though it's only used if
|theme| hasn't yet been initialized. Consider putting this inline where
|thickness| is, or if that doesn't fit well, extracting it to a function that
you can invoke there.

[bokan, 2016/10/18 21:59:52]

Good catch, done.

+                        ->themeEngine()
+                        ->getSize(WebThemeEngine::PartScrollbarVerticalThumb)
+                        .width;
     DEFINE_STATIC_LOCAL(ScrollbarThemeOverlay, theme,
-                        (10, 0, ScrollbarThemeOverlay::AllowHitTest));
+                        (thickness, 0, ScrollbarThemeOverlay::AllowHitTest));
     return theme;
   }
 
   DEFINE_STATIC_LOCAL(ScrollbarThemeAura, theme, ());
   return theme;
 }
 
 int ScrollbarThemeAura::scrollbarThickness(ScrollbarControlSize controlSize) {
   // Horiz and Vert scrollbars are the same thickness.
   // In unit tests we don't have the mock theme engine (because of layering
@@ skipping 238 matching lines @@
   }
 
   // HorizontalScrollbar
   int squareSize = scrollbar.height();
   return IntSize(
       scrollbar.width() < 2 * squareSize ? scrollbar.width() / 2 : squareSize,
       squareSize);
 }
 
 }  // namespace blink