Chromium side for using overlay scrollbars on Aura or Linux.

Add the command line flag --enable-overlay-scrollbars to enable
overlay scrollbars in Aura and Linux.

BUG=None

Review URL: https://chromiumcodereview.appspot.com/22422010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@217100 0039d316-1c4b-4281-b951-d872f2087c98

content/browser/renderer_host/render_process_host_impl.cc

@@ -932,6 +932,7 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     switches::kEnableGpuClientTracing,
     switches::kEnableGpuBenchmarking,
     switches::kEnableMemoryBenchmarking,
+    switches::kEnableOverlayScrollbars,
     switches::kEnableSkiaBenchmarking,
     switches::kEnableLogging,
     switches::kEnableSpeechSynthesis,

content/child/runtime_features.cc

@@ -135,6 +135,9 @@ void SetRuntimeFeaturesDefaultsAndUpdateFromArgs(
 
   if (command_line.HasSwitch(switches::kEnableHTMLImports))
     WebRuntimeFeatures::enableHTMLImports(true);
+
+  if (command_line.HasSwitch(switches::kEnableOverlayScrollbars))
+    WebRuntimeFeatures::enableOverlayScrollbars(true);
 }
 
 }  // namespace content

content/public/common/content_switches.cc

@@ -424,6 +424,9 @@ const char kEnableNewMediaInternals[]       = "enable-new-media-internals";
 // Enables use of cache if offline, even if it's stale
 const char kEnableOfflineCacheAccess[]      = "enable-offline-cache-access";
 
+// Enables overlay scrollbars on Aura or Linux. Does nothing on Mac.
+const char kEnableOverlayScrollbars[]       = "enable-overlay-scrollbars";
+
 // Forward overscroll event data from the renderer to the browser.
 const char kEnableOverscrollNotifications[] = "enable-overscroll-notifications";
 

content/public/common/content_switches.h

@@ -130,6 +130,7 @@ extern const char kEnableMemoryBenchmarking[];
 extern const char kEnableMonitorProfile[];
 extern const char kEnableNewMediaInternals[];
 CONTENT_EXPORT extern const char kEnableOfflineCacheAccess[];
+extern const char kEnableOverlayScrollbars[];
 CONTENT_EXPORT extern const char kEnableOverscrollNotifications[];
 extern const char kEnablePinch[];
 extern const char kEnablePreparsedJsCaching[];

content/renderer/gpu/render_widget_compositor.cc

@@ -277,6 +277,13 @@ scoped_ptr<RenderWidgetCompositor> RenderWidgetCompositor::Create(
   // 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))