Reapply: [oilpan]: Change marking to do precise roots first and conservative

Reapply: https://codereview.chromium.org/405403003/

This change did not contain the bug it just made it much more likely that we would see it. Reapplying (again). :)

original description:

"[oilpan]: Change marking to do precise roots first and conservative second.

This way we avoid conservatively scanning objects that were reachable through precise pointers."

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180188

[Mads Ager (chromium), 2014-08-13 11:20:36]

Created Revert of Revert of Revert "Revert of [oilpan]: Change marking to do
precise roots first and conservative

[haraken, 2014-08-13 11:23:11]

LGTM

[Mads Ager (chromium), 2014-08-13 14:28:45]

The CQ bit was checked by ager@chromium.org

[commit-bot: I haz the power, 2014-08-13 14:30:17]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ager@chromium.org/468083002/150001

[commit-bot: I haz the power, 2014-08-13 15:40:01]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/22558)

[commit-bot: I haz the power, 2014-08-13 16:19:07]

Committed patchset #2 (150001) as 180188