Adding ElementsAccessor::Splice

Adding ElementsAccessor Splice
- remove the Backing-Store specific code from builtins.cc and put it in elements.cc.
- adding tests to improve coverage of the splice method

BUG=

Committed: https://crrev.com/8198610d5d7c6ca205c2e32233a5f4a82213adfa
Cr-Commit-Position: refs/heads/master@{#30410}

[Camillo Bruni, 2015-08-27 10:49:24]

The CQ bit was checked by cbruni@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-27 10:49:29]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1312033003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1312033003/1

[Camillo Bruni, 2015-08-27 10:49:45]

The CQ bit was unchecked by cbruni@chromium.org

[Camillo Bruni, 2015-08-27 11:30:01]

cbruni@chromium.org changed reviewers:
+ yangguo@chromium.org

[Camillo Bruni, 2015-08-27 11:30:01]

PTAL
slightly improved version of https://codereview.chromium.org/1293683005 mainly
adding hole-ing out spliced-off values (which correctly caused a failure in the
blink layout tests)

[Yang, 2015-08-27 11:40:57]

lgtm with comments.

https://codereview.chromium.org/1312033003/diff/60001/src/builtins.cc
File src/builtins.cc (right):

https://codereview.chromium.org/1312033003/diff/60001/src/builtins.cc#newcode169
src/builtins.cc:169: // This is an extended version of ECMA-262 9.4, but
additionally
This seems to refer to spec version 5.1. Is there an equivalent in version 6.0?
7.1.11 seems related.

https://codereview.chromium.org/1312033003/diff/60001/src/builtins.cc#newcode175
src/builtins.cc:175: *out = FastD2IChecked(HeapNumber::cast(object)->value());
Do we have test cases to guarantee that this rounds correctly for positive and
negative numbers? If not, can we have some?

https://codereview.chromium.org/1312033003/diff/60001/src/builtins.cc#newcode181
src/builtins.cc:181: *out = (Oddball::cast(object)->kind() == Oddball::kTrue) ?
1 : 0;
You can use object->IsTrue here.

[Camillo Bruni, 2015-08-27 12:29:12]

The CQ bit was checked by cbruni@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-08-27 12:29:20]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1312033003/80001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1312033003/80001

[commit-bot: I haz the power, 2015-08-27 13:04:09]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-27 13:04:09]

Dry run: This issue passed the CQ dry run.

[Camillo Bruni, 2015-08-27 13:04:30]

The CQ bit was checked by cbruni@chromium.org

[Camillo Bruni, 2015-08-27 13:04:30]

The patchset sent to the CQ was uploaded after l-g-t-m from yangguo@chromium.org
Link to the patchset: https://codereview.chromium.org/1312033003/#ps80001
(title: "addressing comments, adding more tests")

[commit-bot: I haz the power, 2015-08-27 13:04:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1312033003/80001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1312033003/80001

[commit-bot: I haz the power, 2015-08-27 13:05:55]

Committed patchset #5 (id:80001)

[commit-bot: I haz the power, 2015-08-27 13:06:14]

Patchset 5 (id:??) landed as
https://crrev.com/8198610d5d7c6ca205c2e32233a5f4a82213adfa
Cr-Commit-Position: refs/heads/master@{#30410}