Correct touch rect hit-test against iframe with scrolled content

Source/core/layout/LayoutPart.cpp

Index: Source/core/layout/LayoutPart.cpp
diff --git a/Source/core/layout/LayoutPart.cpp b/Source/core/layout/LayoutPart.cpp
index 1f21e6f37993227580d6f39d4d2a665acaf6a9b8..f984289626dd96a3c8499242d1041fbb0cb4dbe2 100644
--- a/Source/core/layout/LayoutPart.cpp
+++ b/Source/core/layout/LayoutPart.cpp
@@ -184,8 +184,19 @@ bool LayoutPart::nodeAtPoint(HitTestResult& result, const HitTestLocation& locat
                 result = childFrameResult;
             }
 
-            if (isInsideChildFrame)
-                return true;
+            // Don't trust |isInsideChildFrame|. Returns true only when the hit test
+            // point/rect is totally within the iframe, i.e. nodeAtPointOverWidget()
+            // also returns true.
+            // Use a temparory HitTestResult because we don't want to collect the
+            // iframe element itself if the hit-test rect is totally within the iframe.
+            if (isInsideChildFrame) {

[dtapuska, 2015/09/08 20:07:48]

I presume this code path isn't necessary for the non rect based hit test..
should it be avoided in that case?


Also is this also an issue for any element that is backed by a ScrollableArea?
ie; does it happen with a div with overflow scroll?

[Yufeng Shen (Slow to review), 2015/09/08 22:08:42]

done.
Yes, the same underlying issue applies also for overflow scroll div,
but the symptom gets mitigated by the fact that we do a re-hit-test
for gesture event, see here

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

The re-hit-test uses hitTestResultInFrame. So if the tap finds the wrong frame,
then the click is routed
to the wrong frame. But if the tap finds at least the correct frame but wrong
node, the click is
still routed to the right node. It is really complicated and subtle :(

+                HitTestResult pointOverWidgetResult = result;
+                bool pointOverWidget = nodeAtPointOverWidget(pointOverWidgetResult, locationInContainer, accumulatedOffset, action);
+                if (pointOverWidget)
+                    return true;
+                result = pointOverWidgetResult;
+                return false;
+            }
         }
     }