Implement elementsFromPoint

Source/core/rendering/HitTestRequest.h

Index: Source/core/rendering/HitTestRequest.h
diff --git a/Source/core/rendering/HitTestRequest.h b/Source/core/rendering/HitTestRequest.h
index 272c0a20222eae54294974dbc9b874fcbcb852bf..a38770f2f580646366075591dc7337ac59c27779 100644
--- a/Source/core/rendering/HitTestRequest.h
+++ b/Source/core/rendering/HitTestRequest.h
@@ -38,6 +38,12 @@ public:
         AllowChildFrameContent = 1 << 8,
         ChildFrameHitTest = 1 << 9,
         IgnorePointerEventsNone = 1 << 10,
+        // Collect a list of nodes instead of just one.
+        // (e.g., for elementsFromPoint or rect-based tests).

[Rick Byers, 2015/02/04 10:34:03]

Is it legal to ask for a list-based hit-test without supplying either an area or
the penetrating flag?

[pdr., 2015/02/17 04:10:13]

It's not, I've updated the comment to be a bit more clear here.

I've also added an assert in HitTestRequest's constructor to enforce this.

[Rick Byers, 2015/02/20 20:02:23]

That enforces the penetrating part, but does anything enforce that you can't ask
for simple list-based with an area of 0?  Either we should enforce that, or just
make it work and return a single-element list.  The latter would avoid adding
new complexity to a few of your callsites  (the hit type could return to being
non-conditional - always list based, area may or may not be zero).

+        ListBased = 1 << 11,
+        // Continues hit testing even after a hit has been found. This is useful
+        // with list-based testing for finding all nodes in an area.
+        Penetrating = 1 << 12,

[Rick Byers, 2015/02/04 10:34:03]

What does it mean to have a penetrating hit test that's not list-based?

[pdr., 2015/02/17 04:10:13]

It doesn't make sense. I've renamed this PenetratingList to make this clearer.

     };
 
     typedef unsigned HitTestRequestType;
@@ -57,6 +63,8 @@ public:
     bool allowsChildFrameContent() const { return m_requestType & AllowChildFrameContent; }
     bool isChildFrameHitTest() const { return m_requestType & ChildFrameHitTest; }
     bool ignorePointerEventsNone() const { return m_requestType & IgnorePointerEventsNone; }
+    bool listBased() const { return m_requestType & ListBased; }
+    bool penetrating() const { return m_requestType & Penetrating; }
 
     // Convenience functions
     bool touchMove() const { return move() && touchEvent(); }