Disable compositing asserts when gesture scrolling on main thread

third_party/WebKit/Source/core/input/ScrollManager.cpp

Index: third_party/WebKit/Source/core/input/ScrollManager.cpp
diff --git a/third_party/WebKit/Source/core/input/ScrollManager.cpp b/third_party/WebKit/Source/core/input/ScrollManager.cpp
index 4ca799892a2a219453212646642ccb51d029d110..ad3296b0f834ffcefe56e529a312d6126f4256bb 100644
--- a/third_party/WebKit/Source/core/input/ScrollManager.cpp
+++ b/third_party/WebKit/Source/core/input/ScrollManager.cpp
@@ -178,7 +178,7 @@ void ScrollManager::customizedScroll(const Node& startNode, ScrollState& scrollS
         return;
 
     if (scrollState.deltaX() || scrollState.deltaY())
-        m_frame->document()->updateStyleAndLayoutIgnorePendingStylesheets();
+        m_frame->view()->updateLifecycleToCompositingCleanPlusScrolling();

[Ian Vollick, 2016/07/06 17:39:18]

I'm worried this is overkill. I spoke with skobes offline and he mentioned that
using an assert disabler is the usual way of dealing with these issues until we
fix the more fundamental issue of fitting scroll properly into the document
lifecycle (eg:
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/layout/La...).
Could we use the same approach here?

 
     if (m_currentScrollChain.empty())
         recomputeScrollChain(startNode, m_currentScrollChain);
@@ -194,10 +194,6 @@ WebInputEventResult ScrollManager::handleGestureScrollBegin(const PlatformGestur
     if (document->layoutViewItem().isNull())
         return WebInputEventResult::NotHandled;
 
-    FrameView* view = m_frame->view();
-    if (!view)
-        return WebInputEventResult::NotHandled;
-
     // If there's no layoutObject on the node, send the event to the nearest ancestor with a layoutObject.
     // Needed for <option> and <optgroup> elements so we can touch scroll <select>s
     while (m_scrollGestureHandlingNode && !m_scrollGestureHandlingNode->layoutObject())
@@ -356,6 +352,9 @@ bool ScrollManager::isEffectiveRootScroller(const Node& node) const
 
 WebInputEventResult ScrollManager::handleGestureScrollEvent(const PlatformGestureEvent& gestureEvent)
 {
+    if (!m_frame->view())
+        return WebInputEventResult::NotHandled;
+
     Node* eventTarget = nullptr;
     Scrollbar* scrollbar = nullptr;
     if (gestureEvent.type() != PlatformEvent::GestureScrollBegin) {