Send scroll animation takeOver message in the same frame that it's created

third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp

Index: third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
diff --git a/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp b/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
index ee693987ba58228eafbed3919ce9910543964adb..5d99eb0d3d947ff914f1f0eaefc38c974d3dda38 100644
--- a/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
+++ b/third_party/WebKit/Source/core/page/scrolling/ScrollingCoordinator.cpp
@@ -662,12 +662,15 @@ void ScrollingCoordinator::setShouldUpdateScrollLayerPositionOnMainThread(MainTh
 {
     if (!m_page->mainFrame()->isLocalFrame() || !m_page->deprecatedLocalMainFrame()->view())
         return;
+
     GraphicsLayer* layer = m_page->deprecatedLocalMainFrame()->view()->layerForScrolling();
     if (WebLayer* scrollLayer = toWebLayer(layer)) {
         m_lastMainThreadScrollingReasons = mainThreadScrollingReasons;
         if (mainThreadScrollingReasons) {
-            if (ScrollAnimatorBase* scrollAnimator = layer->getScrollableArea()->existingScrollAnimator())
+            if (ScrollAnimatorBase* scrollAnimator = layer->getScrollableArea()->existingScrollAnimator()) {
+                DCHECK(m_page->deprecatedLocalMainFrame()->document()->lifecycle().state() >= DocumentLifecycle::CompositingClean);

[jbroman, 2016/06/23 19:12:27]

nit: suggest DCHECK_GE for nicer error messages

                 scrollAnimator->takeOverCompositorAnimation();
+            }
             scrollLayer->addMainThreadScrollingReasons(mainThreadScrollingReasons);
         } else {
             // Clear all main thread scrolling reasons except the one that's set