[builtins] Add an initial fast-path to Object.assign.

[builtins] Add an initial fast-path to Object.assign.

In the case of a simple fast-mode receiver without fancy properties, we
can just walk over the descriptor array to find all its initial property
names. As long as the map stays the same, we can also use that
descriptor array to figure out how to handle the properties.

This speeds up
https://github.com/kpdecker/six-speed/tree/master/tests/object-assign by
~2x.

BUG=

Committed: https://crrev.com/6b89c6941b13373a7ab1c484bddffcd9d0fea559
Cr-Commit-Position: refs/heads/master@{#33895}

[Toon Verwaest, 2016-02-11 10:57:31]

verwaest@chromium.org changed reviewers:
+ bmeurer@chromium.org, cbruni@chromium.org

[Toon Verwaest, 2016-02-11 10:57:31]

cbruni: PTAL
bmeurer: FYI

[Benedikt Meurer, 2016-02-11 11:28:36]

LGTM, nice

[Toon Verwaest, 2016-02-11 12:40:10]

The CQ bit was checked by verwaest@chromium.org

[commit-bot: I haz the power, 2016-02-11 12:40:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1688953004/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1688953004/20001

[Camillo Bruni, 2016-02-11 13:03:54]

lgtm

https://codereview.chromium.org/1688953004/diff/20001/src/objects.cc
File src/objects.cc (right):

https://codereview.chromium.org/1688953004/diff/20001/src/objects.cc#newcode8556
src/objects.cc:8556: bool cache_enum_length = map->OnlyHasSimpleProperties();
yay! readable code :)

[commit-bot: I haz the power, 2016-02-11 13:17:20]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-02-11 13:19:00]

Description was changed from

==========
[builtins] Add an initial fast-path to Object.assign.

In the case of a simple fast-mode receiver without fancy properties, we
can just walk over the descriptor array to find all its initial property
names. As long as the map stays the same, we can also use that
descriptor array to figure out how to handle the properties.

This speeds up
https://github.com/kpdecker/six-speed/tree/master/tests/object-assign by
~2x.

BUG=
==========

to

==========
[builtins] Add an initial fast-path to Object.assign.

In the case of a simple fast-mode receiver without fancy properties, we
can just walk over the descriptor array to find all its initial property
names. As long as the map stays the same, we can also use that
descriptor array to figure out how to handle the properties.

This speeds up
https://github.com/kpdecker/six-speed/tree/master/tests/object-assign by
~2x.

BUG=

Committed: https://crrev.com/6b89c6941b13373a7ab1c484bddffcd9d0fea559
Cr-Commit-Position: refs/heads/master@{#33895}
==========

[commit-bot: I haz the power, 2016-02-11 13:19:01]

Patchset 2 (id:??) landed as
https://crrev.com/6b89c6941b13373a7ab1c484bddffcd9d0fea559
Cr-Commit-Position: refs/heads/master@{#33895}