Add a flag for enabling/disabling the new accelerated scrolling path

content/renderer/render_view_impl.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 "content/renderer/render_view_impl.h"
 
 #include <algorithm>
 #include <cmath>
 
 #include "base/auto_reset.h"
@@ skipping 621 matching lines @@
 
   if (command_line.HasSwitch(switches::kEnableCompositedScrollingForFrames))
     return true;
 
   if (!cc::switches::IsLCDTextEnabled())
     return true;
 
   return DeviceScaleEnsuresTextQuality(device_scale_factor);
 }
 
+static bool ShouldUseUniversalAcceleratedCompositingForOverflowScroll() {
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+
+  if (command_line.HasSwitch(
+          switches::kDisableUniversalAcceleratedOverflowScroll))
+    return false;
+
+  if (command_line.HasSwitch(
+          switches::kEnableUniversalAcceleratedOverflowScroll))
+    return true;
+
+  return false;
+}
+
 static bool ShouldUseTransitionCompositing(float device_scale_factor) {
   const CommandLine& command_line = *CommandLine::ForCurrentProcess();
 
   if (command_line.HasSwitch(switches::kDisableCompositingForTransition))
     return false;
 
   if (command_line.HasSwitch(switches::kEnableCompositingForTransition))
     return true;
 
   // TODO(ajuma): Re-enable this by default for high-DPI once the problem
@@ skipping 269 matching lines @@
     CompleteInit();
   }
 
   g_view_map.Get().insert(std::make_pair(webview(), this));
   g_routing_id_view_map.Get().insert(std::make_pair(routing_id_, this));
   webview()->setDeviceScaleFactor(device_scale_factor_);
   webview()->settings()->setAcceleratedCompositingForFixedPositionEnabled(
       ShouldUseFixedPositionCompositing(device_scale_factor_));
   webview()->settings()->setAcceleratedCompositingForOverflowScrollEnabled(
       ShouldUseAcceleratedCompositingForOverflowScroll(device_scale_factor_));
+  webview()->settings()->setCompositorDrivenAcceleratedScrollingEnabled(
+      ShouldUseUniversalAcceleratedCompositingForOverflowScroll());
   webview()->settings()->setAcceleratedCompositingForTransitionEnabled(
       ShouldUseTransitionCompositing(device_scale_factor_));
   webview()->settings()->setAcceleratedCompositingForFixedRootBackgroundEnabled(
       ShouldUseAcceleratedFixedRootBackground(device_scale_factor_));
   webview()->settings()->setAcceleratedCompositingForScrollableFramesEnabled(
       ShouldUseAcceleratedCompositingForScrollableFrames(device_scale_factor_));
   webview()->settings()->setCompositedScrollingForFramesEnabled(
       ShouldUseCompositedScrollingForFrames(device_scale_factor_));
 
   ApplyWebPreferences(webkit_preferences_, webview());
@@ skipping 5660 matching lines @@
   for (size_t i = 0; i < icon_urls.size(); i++) {
     WebURL url = icon_urls[i].iconURL();
     if (!url.isEmpty())
       urls.push_back(FaviconURL(url,
                                 ToFaviconType(icon_urls[i].iconType())));
   }
   SendUpdateFaviconURL(urls);
 }
 
 }  // namespace content