Remove EventHandler::m_didStartDrag.

Remove EventHandler::m_didStartDrag.

EventHandler maintains a ton of state, and making sure everything is in
sync gets rather complicated. m_didStartDrag was only used as by gesture
code, to detect if it should fall back to default handling.

This patch changes handleDrag()'s CheckDragHysteresis parameter to
DragIniator, which more accurately reflects how it's used. The updated
parameter is also used to determine when default handling is needed,
eliminating the need for the m_didStartDrag bool. Yay!

BUG=none

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=185337

[dcheng, 2014-11-13 21:29:57]

dcheng@chromium.org changed reviewers:
+ rbyers@chromium.org

[dcheng, 2014-11-13 21:29:57]

Now EventHandler only has 51 members instead of 52!

[Rick Byers, 2014-11-13 22:14:05]

Thanks for the clean-up! LGTM

[dcheng, 2014-11-13 22:15:07]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2014-11-13 22:15:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/720693003/1

[commit-bot: I haz the power, 2014-11-14 00:03:52]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-11-14 00:03:54]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/36418)

[dcheng, 2014-11-14 00:07:34]

The CQ bit was checked by dcheng@chromium.org

[commit-bot: I haz the power, 2014-11-14 00:08:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/720693003/1

[commit-bot: I haz the power, 2014-11-14 00:57:39]

Committed patchset #1 (id:1) as 185337