http://crrev.com/2610023002, which is a speculative fix for http://crbug.com/677916, assumes that it is possible for the renderer to receive a DragMsg_TargetDragLeave before a mouse movement exceeds the threshold needed to start a dragging operation.

Per [1], this is a violation of the invariants in the browser->renderer IPC interface around Drag-and-Drop, and should be investigated.

[1] https://codereview.chromium.org/2610023002/diff/20001/third_party/WebKit/Source/core/input/EventHandlerTest.cpp#newcode279