Add a UseCounter for Object.observe

Add a UseCounter for Object.observe

It triggers once per context that calls observe (or attempts to access
any observation metadata, e.g. through Object.getNotifier).

Committed: https://crrev.com/729b85ae8678ebd998a0e5f254817683198d0610
Cr-Commit-Position: refs/heads/master@{#27557}

[adamk, 2015-03-31 19:05:52]

adamk@chromium.org changed reviewers:
+ arv@chromium.org

[arv (Not doing code reviews), 2015-03-31 19:17:12]

LGTM

[adamk, 2015-03-31 22:22:25]

So this patch is fine by itself, but we'll need something fancier on the Blink
side to properly identify the responsible ExecutionContext. The current code
uses GetCallingContext(), but that gives the builtins context for this example,
which then crashes when it can't find a V8PerContextData embedded there.

[adamk, 2015-03-31 22:29:56]

I misdiagnosed the problem, it was simply a lack of a HandleScope that was
causing problems. See patchset 2.

[arv (Not doing code reviews), 2015-03-31 22:38:27]

Still LGTM

[adamk, 2015-03-31 22:41:52]

On 2015/03/31 22:38:27, arv wrote:
> Still LGTM

Hmm, I think this HandleScope is actually in the wrong place. The Blink code is
just wrong, and should itself create a HandleScope. But this is safer anyway.

[adamk, 2015-03-31 22:42:04]

The CQ bit was checked by adamk@chromium.org

[commit-bot: I haz the power, 2015-03-31 22:42:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1048213002/20001

[commit-bot: I haz the power, 2015-03-31 23:03:13]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-31 23:03:25]

Patchset 2 (id:??) landed as
https://crrev.com/729b85ae8678ebd998a0e5f254817683198d0610
Cr-Commit-Position: refs/heads/master@{#27557}