Add Oilpan heap object headers.

Will start pulling things in so we can get objects allocated
in the oilpan heap with Persistent handles to them.

R=vegorov@chromium.org
BUG=

Review URL: https://codereview.chromium.org/99923006

git-svn-id: svn://svn.chromium.org/blink/trunk@163786 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert of https://codereview.chromium.org/93603003/
Reason for revert: 100 layout tests are crashing on debug builds garden-o-matic blames this patch.  Crash logs look V8 related.

TBR=yurys@chromium.org,aandrey@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/108413005

git-svn-id: svn://svn.chromium.org/blink/trunk@163787 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert of https://codereview.chromium.org/108413005/
Reason for revert: Reverting the revert.  Original patch was not to blame after all.

TBR=yurys@chromium.org,aandrey@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/105633004

git-svn-id: svn://svn.chromium.org/blink/trunk@163789 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: Do not invoke HashMap.get(NULL) in AsyncCallStackTracker.

The contextDestroyed method of the LifecycleObserver can pass
a (valid) ExecutionContext* NULL pointer.
Do not do a lookup into the HashMap in this case.

R=yurys@chromium.org, yurys

Review URL: https://codereview.chromium.org/109613008

git-svn-id: svn://svn.chromium.org/blink/trunk@163790 bbb929c8-8fbe-4397-9dbb-9b2b20218538