Fix crasher in the pdf tear down code path.

Fix crasher in the pdf tear down code path.

The crash occurs because of a timer dereferencing a null engine pointer.
The crash appears to have occurred due to this patch https://codereview.chromium.org/427583003/

Fix is to cancel all timers when the pdf instance is being torn down before
destroying the engine.

BUG=403036
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=289218

[Tom Sepez, 2014-08-12 23:28:09]

LGTM. Thanks for catching this.

[ananta, 2014-08-12 23:31:08]

+jam for pdf owners stamp

[jam, 2014-08-13 00:09:15]

lgtm

[ananta, 2014-08-13 00:10:34]

The CQ bit was checked by ananta@chromium.org

[commit-bot: I haz the power, 2014-08-13 00:18:29]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ananta@chromium.org/462283002/1

[commit-bot: I haz the power, 2014-08-13 01:28:28]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[commit-bot: I haz the power, 2014-08-13 01:42:30]

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

[commit-bot: I haz the power, 2014-08-13 01:42:31]

Try jobs failed on following builders:
  win_chromium_x64_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[ananta, 2014-08-13 01:44:04]

The CQ bit was checked by ananta@chromium.org

[commit-bot: I haz the power, 2014-08-13 01:49:32]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ananta@chromium.org/462283002/1

[commit-bot: I haz the power, 2014-08-13 08:52:10]

Change committed as 289218