Fallback to root layer if hit-testing does not hit anything in iframe

Source/core/paint/DeprecatedPaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1473 matching lines @@
 
     const HitTestRequest& request = result.hitTestRequest();
     const HitTestLocation& hitTestLocation = result.hitTestLocation();
 
     // Start with frameVisibleRect to ensure we include the scrollbars.
     LayoutRect hitTestArea = frameVisibleRect(layoutObject());
     if (request.ignoreClipping())
         hitTestArea.unite(LayoutRect(layoutObject()->view()->documentRect()));
 
     DeprecatedPaintLayer* insideLayer = hitTestLayer(this, 0, result, hitTestArea, hitTestLocation, false);
-    if (!insideLayer) {
-        // We didn't hit any layer. If we are the root layer and the mouse is -- or just was -- down,
-        // return ourselves. We do this so mouse events continue getting delivered after a drag has
-        // exited the WebView, and so hit testing over a scrollbar hits the content document.
-        // In addtion, it is possible for the mouse to stay in the document but there is no element.
-        // At that time, the events of the mouse should be fired.
+    if (!insideLayer && isRootLayer()) {
         // TODO(majidvp): This should apply more consistently across different event types and we

[Rick Byers, 2015/08/20 19:28:22]

nit: please move this TODO to your second case - it doesn't apply to your first
block.

[Yufeng Shen (Slow to review), 2015/08/20 20:28:19]

Done.

         // should not use RequestType for it. Perhaps best for it to be done at a higher level. See
         // http://crbug.com/505825
-        LayoutPoint hitPoint = hitTestLocation.point();
-        if (!request.isChildFrameHitTest() && ((request.active() || request.release()) || (request.move() && hitTestArea.contains(hitPoint.x(), hitPoint.y()))) && isRootLayer()) {
+
+        IntRect hitRect = hitTestLocation.boundingBox();
+        bool fallback = false;
+        // If we didn't hit any layers but are still inside the document
+        // bounds, then we should fallback to hitting the document.
+        // For rect-based hit test, we do the fallback only when the hit-rect
+        // is totally within the document bounds.
+        if (hitTestArea.contains(LayoutRect(hitRect))) {
+            fallback = true;
+        // Mouse dragging outside the main document should also be

[Rick Byers, 2015/08/20 19:28:22]

nit: add a newline above here to make the separation of the two (very different)
cases more clear.

[Yufeng Shen (Slow to review), 2015/08/20 20:28:19]

Done.

+        // delivered to the document.
+        // TODO(miletus): Capture behavior inconsistent with iframes
+        // crbug.com/522109.
+        } else if ((request.active() || request.release()) && !request.isChildFrameHitTest()) {
+            fallback = true;
+        }
+        if (fallback) {
             layoutObject()->updateHitTestResult(result, toLayoutView(layoutObject())->flipForWritingMode(hitTestLocation.point()));
             insideLayer = this;
 
             // Don't cache this result since it really wasn't a true hit.
             result.setCacheable(false);
         }
     }
 
     // Now determine if the result is inside an anchor - if the urlElement isn't already set.
     Node* node = result.innerNode();
@@ skipping 1156 matching lines @@
 
 void showLayerTree(const blink::LayoutObject* layoutObject)
 {
     if (!layoutObject) {
         fprintf(stderr, "Cannot showLayerTree. Root is (nil)\n");
         return;
     }
     showLayerTree(layoutObject->enclosingLayer());
 }
 #endif