Chromium side plumbing for enabling fixed root background compositing.

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 6851b4e6200d69d6548b252321ba3842e8e9f4b6..542375d841919910da523e62e4ab62e4bc5e71b0 100644
--- a/content/renderer/render_view_impl.cc
+++ b/content/renderer/render_view_impl.cc
@@ -605,6 +605,18 @@ static bool ShouldUseTransitionCompositing(float device_scale_factor) {
   return DeviceScaleEnsuresTextQuality(device_scale_factor);
 }
 
+static bool ShouldUseAcceleratedFixedRootBackground(float device_scale_factor) {
+  const CommandLine& command_line = *CommandLine::ForCurrentProcess();
+
+  if (command_line.HasSwitch(switches::kDisableAcceleratedFixedRootBackground))
+    return false;
+
+  if (command_line.HasSwitch(switches::kEnableAcceleratedFixedRootBackground))
+    return true;
+
+  return DeviceScaleEnsuresTextQuality(device_scale_factor);
+}
+
 static FaviconURL::IconType ToFaviconType(WebKit::WebIconURL::Type type) {
   switch (type) {
     case WebKit::WebIconURL::TypeFavicon:
@@ -878,6 +890,8 @@ void RenderViewImpl::Initialize(RenderViewImplParams* params) {
       ShouldUseFixedPositionCompositing(device_scale_factor_));
   webview()->settings()->setAcceleratedCompositingForTransitionEnabled(
       ShouldUseTransitionCompositing(device_scale_factor_));
+  webview()->settings()->setAcceleratedCompositingForFixedRootBackgroundEnabled(
+      ShouldUseAcceleratedFixedRootBackground(device_scale_factor_));
 
   webkit_glue::ApplyWebPreferences(webkit_preferences_, webview());
   webview()->initializeMainFrame(this);
@@ -6197,6 +6211,9 @@ void RenderViewImpl::SetDeviceScaleFactor(float device_scale_factor) {
         ShouldUseFixedPositionCompositing(device_scale_factor_));
     webview()->settings()->setAcceleratedCompositingForTransitionEnabled(
         ShouldUseTransitionCompositing(device_scale_factor_));
+    webview()->settings()->
+        setAcceleratedCompositingForFixedRootBackgroundEnabled(
+            ShouldUseAcceleratedFixedRootBackground(device_scale_factor_));
   }
   if (auto_resize_mode_)
     AutoResizeCompositor();