Don't update main thread scroll reasons on a throttled frame.

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index 9c2a250fdc0917d248438f7d1e7bfd841be0f1ef..26314318f1e8ebc1f868159cd7d8ba08b14ac9e7 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -4888,10 +4888,13 @@ void FrameView::updateSubFrameScrollOnMainReason(
   if (!frame.isLocalFrame())
     return;
 
-  if (!toLocalFrame(frame).view()->layerForScrolling())
+  FrameView& frameView = *toLocalFrame(frame).view();
+  if (frameView.shouldThrottleRendering())
+    return;
+  if (!frameView.layerForScrolling())
     return;
 
-  reasons |= toLocalFrame(frame).view()->mainThreadScrollingReasonsPerFrame();
+  reasons |= frameView.mainThreadScrollingReasonsPerFrame();
   if (GraphicsLayer* layerForScrolling = toLocalFrame(frame)
                                              .view()
                                              ->layoutViewportScrollableArea()