Add a flag to disable threaded scrolling

content/renderer/render_view_impl.cc

Index: content/renderer/render_view_impl.cc
diff --git a/content/renderer/render_view_impl.cc b/content/renderer/render_view_impl.cc
index eba0382f3453be34ace76c5ecbc5423274f14451..4c216957e87fc8a7bafa262d879dfe3eaad0b75c 100644
--- a/content/renderer/render_view_impl.cc
+++ b/content/renderer/render_view_impl.cc
@@ -422,6 +422,15 @@ static bool ShouldUseTransitionCompositing(float device_scale_factor) {
   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:
@@ -759,6 +768,8 @@ void RenderViewImpl::Initialize(RenderViewImplParams* params) {
       PreferCompositingToLCDText(device_scale_factor_));
   webview()->settings()->setAcceleratedCompositingForTransitionEnabled(
       ShouldUseTransitionCompositing(device_scale_factor_));
+  webview()->settings()->setThreadedScrollingEnabled(
+      ShouldUseThreadedScrolling());
 
   ApplyWebPreferences(webkit_preferences_, webview());