Add a flag to disable threaded scrolling

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 404 matching lines @@
 
   if (command_line.HasSwitch(switches::kEnableCompositingForTransition))
     return true;
 
   // TODO(ajuma): Re-enable this by default for high-DPI once the problem
   // of excessive layer promotion caused by overlap has been addressed.
   // http://crbug.com/178119.
   return false;
 }
 
+static bool ShouldUseThreadedScrolling() {

[jam, 2014/09/23 05:12:59]

this should be inlined, we normally don't add methods to CommandLine::HasSwitch.
the caller also already has command_line

[jdduke (slow), 2014/09/23 19:18:11]

Done.

+  if (CommandLine::ForCurrentProcess()
+          ->HasSwitch(switches::kDisableThreadedScrolling)) {
+    return false;
+  }
+
+  return true;
+}
+
 static FaviconURL::IconType ToFaviconType(blink::WebIconURL::Type type) {
   switch (type) {
     case blink::WebIconURL::TypeFavicon:
       return FaviconURL::FAVICON;
     case blink::WebIconURL::TypeTouch:
       return FaviconURL::TOUCH_ICON;
     case blink::WebIconURL::TypeTouchPrecomposed:
       return FaviconURL::TOUCH_PRECOMPOSED_ICON;
     case blink::WebIconURL::TypeInvalid:
       return FaviconURL::INVALID_ICON;
@@ skipping 317 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()->setPreferCompositingToLCDTextEnabled(
       PreferCompositingToLCDText(device_scale_factor_));
   webview()->settings()->setAcceleratedCompositingForTransitionEnabled(
       ShouldUseTransitionCompositing(device_scale_factor_));
+  webview()->settings()->setThreadedScrollingEnabled(
+      ShouldUseThreadedScrolling());
 
   ApplyWebPreferences(webkit_preferences_, webview());
 
   webview()->settings()->setAllowConnectingInsecureWebSocket(
       command_line.HasSwitch(switches::kAllowInsecureWebSocketFromHttpsOrigin));
 
   RenderFrameProxy* proxy = NULL;
   if (params->proxy_routing_id != MSG_ROUTING_NONE) {
     CHECK(params->swapped_out);
     proxy = RenderFrameProxy::CreateProxyToReplaceFrame(
@@ skipping 3444 matching lines @@
     std::vector<gfx::Size> sizes;
     ConvertToFaviconSizes(icon_urls[i].sizes(), &sizes);
     if (!url.isEmpty())
       urls.push_back(
           FaviconURL(url, ToFaviconType(icon_urls[i].iconType()), sizes));
   }
   SendUpdateFaviconURL(urls);
 }
 
 }  // namespace content