Fix hit testing to be aware of inert inlines.

Source/core/rendering/RenderObject.cpp

Index: Source/core/rendering/RenderObject.cpp
diff --git a/Source/core/rendering/RenderObject.cpp b/Source/core/rendering/RenderObject.cpp
index fb211b88f2b49934cfb7581e51e6c98702595bdd..8a2cf8bd704916ac0e0edfd388b877a3b29a4468 100644
--- a/Source/core/rendering/RenderObject.cpp
+++ b/Source/core/rendering/RenderObject.cpp
@@ -2956,6 +2956,17 @@ AnimationController* RenderObject::animation() const
     return frame()->animation();
 }
 
+bool RenderObject::isInert() const

[Hajime Morrita, 2013/06/03 03:28:35]

Having these kind of loops here smells wrong, especially
- hit testing is tree traversal and can be hot operation
- in most of the case the result is false.

Can we have some fast paths here?
For example, it seems that this is always false if document dosn't have any
active dialog.

[falken, 2013/06/03 03:47:55]

Right, I had thought about a fast path like that but I figured it's at most a
couple hops to the nearest ancestor element node, and someday isInert should
support the 'inert' attribute. Well, I'll try experimenting with a fast path and
see if I can measure an improvement.

[falken, 2013/06/04 04:33:26]

Through some quick benchmarking, I don't think isInert meaningfully
impacts hit testing performance. visibleToHitTesting does take some
hit but end-to-end it doesn't seem to matter. Specifically, on my
machine 10,000 iterations of visibleToHitTesting increases from ~10ms
(if isInert is not called) to about 20-30ms, but no impact is seen on
my benchmark of mouse movement at
https://codereview.chromium.org/16347002/
(not really in a state to be committed to the tree).

+{
+    const RenderObject* renderer = this;
+    while (!renderer->node())
+        renderer = renderer->parent();
+    const Node* parentNode = renderer->node();
+    while (parentNode && !parentNode->isElementNode())
+        parentNode = parentNode->parentNode();
+    return parentNode && toElement(parentNode)->isInert();
+}
+
 void RenderObject::imageChanged(CachedImage* image, const IntRect* rect)
 {
     imageChanged(static_cast<WrappedImagePtr>(image), rect);