Chromium side for using overlay scrollbars on Aura or Linux.

content/renderer/gpu/render_widget_compositor.cc

 // Copyright (c) 2013 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/renderer/gpu/render_widget_compositor.h"
 
 #include <limits>
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 259 matching lines @@
   settings.solid_color_scrollbars = true;
   settings.solid_color_scrollbar_color =
       cmd->HasSwitch(switches::kHideScrollbars)
           ? SK_ColorTRANSPARENT
           : SkColorSetARGB(128, 128, 128, 128);
   settings.solid_color_scrollbar_thickness_dip = 3;
   settings.highp_threshold_min = 2048;
   // Android WebView handles root layer flings itself.
   settings.ignore_root_layer_flings =
       widget->UsingSynchronousRendererCompositor();
+#elif !defined(OS_MACOSX)
+  if (cmd->HasSwitch(switches::kEnableOverlayScrollbars)) {
+    settings.use_linear_fade_scrollbar_animator = true;
+    settings.solid_color_scrollbars = true;
+    settings.solid_color_scrollbar_color = SkColorSetARGB(128, 128, 128, 128);
+    settings.solid_color_scrollbar_thickness_dip = 3;
+  }
 #endif
 
   if (!compositor->initialize(settings))
     return scoped_ptr<RenderWidgetCompositor>();
 
   return compositor.Pass();
 }
 
 RenderWidgetCompositor::RenderWidgetCompositor(RenderWidget* widget,
                                                bool threaded)
@@ skipping 286 matching lines @@
   return RenderThreadImpl::current()->OffscreenContextProviderForMainThread();
 }
 
 scoped_refptr<cc::ContextProvider>
 RenderWidgetCompositor::OffscreenContextProviderForCompositorThread() {
   return RenderThreadImpl::current()->
       OffscreenContextProviderForCompositorThread();
 }
 
 }  // namespace content