Document::updateHoverActiveState only cancel hover and active state when hitting native scrollbar

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
@@ skipping 3505 matching lines @@
   // page.  Furthermore, mousemove events before the first layout should not
   // lead to a premature layout() happening, which could show a flash of white.
   // See also the similar code in EventHandler::hitTestResultAtPoint.
   if (layoutViewItem().isNull() || !view() || !view()->didFirstLayout())
     return MouseEventWithHitTestResults(event,
                                         HitTestResult(request, LayoutPoint()));
 
   HitTestResult result(request, documentPoint);
   layoutViewItem().hitTest(result);
 
-  if (!request.readOnly())
-    updateHoverActiveState(request, result.innerElement(), result.scrollbar());
+  if (!request.readOnly()) {
+    updateHoverActiveState(
+        request, result.innerElement(),
+        result.scrollbar() && result.scrollbar()->isOverlayScrollbar());
+  }
 
   if (isHTMLCanvasElement(result.innerNode())) {
     PlatformMouseEvent eventWithRegion = event;
     HitTestCanvasResult* hitTestCanvasResult =
         toHTMLCanvasElement(result.innerNode())
             ->getControlAndIdIfHitRegionExists(result.pointInInnerNodeFrame());
     if (hitTestCanvasResult->getControl()) {
       result.setInnerNode(hitTestCanvasResult->getControl());
     }
     eventWithRegion.setRegion(hitTestCanvasResult->getId());
@@ skipping 2474 matching lines @@
       if (currObj1 == currObj2)
         return currObj1;
     }
   }
 
   return 0;
 }
 
 void Document::updateHoverActiveState(const HitTestRequest& request,
                                       Element* innerElement,
-                                      bool hitScrollbar) {
+                                      bool hitOverlayScrollbar) {

[bokan, 2016/11/23 15:07:50]

I think the distinction is native vs custom rather than overlay vs non-overlay,
right? I'm guessing what's happening is that a custom scrollbar takes the
document's :hover state but we clear that below if we hit a scrollbar. A native
scrollbar doesn't take :hover states so we should be checking for custom
scrollbars.

In any case, please replace this bool with Scrollbar* hitScrollbar. You can then
check in this method if its non-null and whether it's custom or not. 

   DCHECK(!request.readOnly());
 
-  if (request.active() && m_frame && !hitScrollbar)
+  if (request.active() && m_frame && !hitOverlayScrollbar)
     m_frame->eventHandler().notifyElementActivated();
 
-  Element* innerElementInDocument = hitScrollbar ? nullptr : innerElement;
+  Element* innerElementInDocument =
+      hitOverlayScrollbar ? nullptr : innerElement;
   while (innerElementInDocument && innerElementInDocument->document() != this) {
     innerElementInDocument->document().updateHoverActiveState(
-        request, innerElementInDocument, hitScrollbar);
+        request, innerElementInDocument, hitOverlayScrollbar);
     innerElementInDocument = innerElementInDocument->document().localOwner();
   }
 
   updateDistribution();
   Element* oldActiveElement = activeHoverElement();
-  if (oldActiveElement && (!request.active() || hitScrollbar)) {
+  if (oldActiveElement && (!request.active() || hitOverlayScrollbar)) {
     // The oldActiveElement layoutObject is null, dropped on :active by setting
     // display: none, for instance. We still need to clear the ActiveChain as
     // the mouse is released.
     for (Node* node = oldActiveElement; node;
          node = FlatTreeTraversal::parent(*node)) {
       DCHECK(!node->isTextNode());
       node->setActive(false);
       m_userActionElements.setInActiveChain(node, false);
     }
     setActiveHoverElement(nullptr);
@@ skipping 474 matching lines @@
 }
 
 void showLiveDocumentInstances() {
   WeakDocumentSet& set = liveDocumentSet();
   fprintf(stderr, "There are %u documents currently alive:\n", set.size());
   for (Document* document : set)
     fprintf(stderr, "- Document %p URL: %s\n", document,
             document->url().getString().utf8().data());
 }
 #endif