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

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

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index c44b227186644837c5a4a628e8e496940d1075d4..8dca1ca509c3aad6df7307f899262ad9e0fb4d5e 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -3523,8 +3523,11 @@ MouseEventWithHitTestResults Document::performMouseEventHitTest(
   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;
@@ -6019,22 +6022,23 @@ static LayoutObject* nearestCommonHoverAncestor(LayoutObject* obj1,
 
 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.