Move the shared timer to be dynamically allocated.

Move the shared timer to be dynamically allocated.

The shared timer must be deleted on the same thread that it was executing on. When the WebThread is being destroyed, it is done from a different thread, so the shared timer must be deleted prior to that. This gives an API for the thread cleanup code to do so.

BUG=301515

[nasko, 2014-07-23 09:42:27]

Hey Jochen,
Can you review this CL for me? 
The crashes I was hitting were DCHECKs because the shared timer was deleted from
a different thread that executed it. This CL adds a way for the thread cleanup
to delete the timer.
Thanks!
Nasko

[jochen (gone - plz use gerrit), 2014-07-23 09:47:25]

lgtm

[nasko, 2014-07-23 09:51:26]

The CQ bit was checked by nasko@chromium.org

[commit-bot: I haz the power, 2014-07-23 09:52:38]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/nasko@chromium.org/416453002/1

[commit-bot: I haz the power, 2014-07-23 11:33:50]

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

[nasko, 2014-07-23 14:26:09]

The CQ bit was unchecked by nasko@chromium.org

[nasko, 2014-07-24 07:18:23]

This landed as r284920, the dcommit tool gave out an error and didn't update
this issue. 

http://src.chromium.org/viewvc/chrome?revision=284920