Merge 58616 - WebCore: Convert m_documentUnderMouse, m_dragInitiator to RefPt...

Merge 58616 - WebCore: Convert m_documentUnderMouse, m_dragInitiator to RefPtr.
Eliminated unused m_dragInitiator accessor to prevent dereferencing.
https://bugs.webkit.org/show_bug.cgi?id=37618

BUG=41469
TEST=drag-drop-iframe-refresh-crash.html

Patch by Abhishek Arya <inferno@chromium.org>; on 20100430
Reviewed by David Kilzer.

Test: editing/pasteboard/dragdropiframerefreshcrash.html

* page/DragController.cpp:
(WebCore::DragController::tryDocumentDrag):
(WebCore::DragController::concludeEditDrag):
* page/DragController.h:
(WebCore::DragController::draggingImageURL):
(WebCore::DragController::documentUnderMouse):

LayoutTests: Tests for a crash when an image dragdrop operation happens inside a continuously refreshing iframe.
https://bugs.webkit.org/show_bug.cgi?id=37618

Patch by Abhishek Arya <inferno@chromium.org>; on 20100430
Reviewed by David Kilzer.

* editing/pasteboard/dragdropiframerefreshcrashexpected.txt: Added.
* editing/pasteboard/dragdropiframerefreshcrash.html: Added.
* editing/resources/dragdrop.html: Added.
* platform/qt/Skipped:

TBR=ddkilzer@apple.com

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=46185