GTK: when doing a drag from a web page, pass a recent mouse down to gtk_drag_...

GTK: when doing a drag from a web page, pass a recent mouse down to gtk_drag_begin() so it has a better idea what time to pass to gdk_grab_pointer().

I believe the following was happening:
- render view gets mouse down, forwards to webkit
- render view gets motion, forwards to webkit
- user releases mouse button, that event is added to the queue
- browser gets message from webkit that a drag has begun, calls gtk_drag_begin() with no event
- gtk_drag_begin initiates a cursor grab, but it only applies to events that have not yet been added to the queue
- mouse release comes up in queue; passed to render view rather than the drag widget

TEST=You can't get stuck in really short render view drags. Whereas it was really easy to repro before (especially in Xephyr), I can repro no longer.
BUG=http://crbug.com/15768


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=19839

[Elliot Glaysher, 2009-07-02 20:04:46]

LGTM + nit

http://codereview.chromium.org/150204/diff/1/2
File chrome/browser/tab_contents/tab_contents_view_gtk.h (right):

http://codereview.chromium.org/150204/diff/1/2#newcode119
Line 119: // The event time for the last mouse down we handled. We need this for
context
s/time//;