Handle root layer fling Java-side in android_webview.

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index 60f26350e8edac6cd3624f5a591812714d053a1e..63d5aa5d7dba81fdac2cfdc8803eae38da3f08ff 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -274,6 +274,9 @@ scoped_ptr<RenderWidgetCompositor> RenderWidgetCompositor::Create(
           : SkColorSetARGB(128, 128, 128, 128);
   settings.solid_color_scrollbar_thickness_dip = 3;
   settings.highp_threshold_min = 2048;
+  // Android WebView handles root layer flings itself.
+  settings.ignore_root_layer_flings =
+      widget->UsingSynchronousRendererCompositor();
 #endif
 
   if (!compositor->initialize(settings))