Disable compositing asserts when gesture scrolling on main thread

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/input/ScrollManager.h"
 
 #include "core/dom/DOMNodeIds.h"
 #include "core/events/GestureEvent.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
@@ skipping 160 matching lines @@
     if (DocumentLoader* documentLoader = m_frame->loader().documentLoader())
         documentLoader->initialScrollState().wasScrolledByUser = true;
 }
 
 void ScrollManager::customizedScroll(const Node& startNode, ScrollState& scrollState)
 {
     if (scrollState.fullyConsumed())
         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);
     scrollState.setScrollChain(m_currentScrollChain);
 
     scrollState.distributeToScrollChainDescendant();
 }
 
 WebInputEventResult ScrollManager::handleGestureScrollBegin(const PlatformGestureEvent& gestureEvent)
 {
     Document* document = m_frame->document();
 
     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())
         m_scrollGestureHandlingNode = m_scrollGestureHandlingNode->parentOrShadowHostNode();
 
     if (!m_scrollGestureHandlingNode)
         m_scrollGestureHandlingNode = m_frame->document()->documentElement();
 
     if (!m_scrollGestureHandlingNode)
         return WebInputEventResult::NotHandled;
@@ skipping 138 matching lines @@
 
     if (!node.isElementNode())
         return false;
 
     return node.isSameNode(m_frame->document()->effectiveRootScroller());
 }
 
 
 WebInputEventResult ScrollManager::handleGestureScrollEvent(const PlatformGestureEvent& gestureEvent)
 {
+    if (!m_frame->view())
+        return WebInputEventResult::NotHandled;
+
     Node* eventTarget = nullptr;
     Scrollbar* scrollbar = nullptr;
     if (gestureEvent.type() != PlatformEvent::GestureScrollBegin) {
         scrollbar = m_scrollbarHandlingScrollGesture.get();
         eventTarget = m_scrollGestureHandlingNode.get();
     }
 
     if (!eventTarget) {
         Document* document = m_frame->document();
         if (document->layoutViewItem().isNull())
@@ skipping 135 matching lines @@
 DEFINE_TRACE(ScrollManager)
 {
     visitor->trace(m_frame);
     visitor->trace(m_scrollGestureHandlingNode);
     visitor->trace(m_previousGestureScrolledNode);
     visitor->trace(m_scrollbarHandlingScrollGesture);
     visitor->trace(m_resizeScrollableArea);
 }
 
 } // namespace blink