[JSON stringifier] Reintroduce fast path with bail out to slow path.

[JSON stringifier] Reintroduce fast path with bail out to slow path.

R=verwaest@chromium.org
BUG=chromium:554946
LOG=N

Committed: https://crrev.com/a7e50a5e06b2c7edd7915df774769c9add42be27
Cr-Commit-Position: refs/heads/master@{#31977}

[Toon Verwaest, 2015-11-13 09:33:23]

lgtm with nit.
please add test that changes elements kind without changing length

https://codereview.chromium.org/1442963002/diff/1/src/json-stringifier.h
File src/json-stringifier.h (right):

https://codereview.chromium.org/1442963002/diff/1/src/json-stringifier.h#newc...
src/json-stringifier.h:472:
Handle<Object>(FixedArray::cast(object->elements())->get(i),
handle(...) works too.

[Yang, 2015-11-13 09:44:57]

fix tests

[Toon Verwaest, 2015-11-13 09:45:30]

lgtm

[Yang, 2015-11-13 09:45:40]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-11-13 09:45:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1442963002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1442963002/40001

[commit-bot: I haz the power, 2015-11-13 10:09:37]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-11-14 23:21:18]

Patchset 3 (id:??) landed as
https://crrev.com/a7e50a5e06b2c7edd7915df774769c9add42be27
Cr-Commit-Position: refs/heads/master@{#31977}