PPC: [es6] Introduce a dedicated JSIteratorResult type.

PPC: [es6] Introduce a dedicated JSIteratorResult type.

Port 72bc4b5c8a5c4279bcb8b340edbc8aa1c46d75a1

Original commit message:
    Use a single JSIteratorResult type for all implementation provided
    iterator results (i.e. the String, Array and collection iterators,
    and also for generators).  This removes one source of unnecessary
    polymorphism in for-of loops.  It is accomplished by a new intrinsic
    %_CreateIterResultObject() that should be used to create iterator
    result objects from JavaScript builtins (there's a matching factory
    method for C++ code).

    Also restructure the %StringIteratorPrototype%.next() and
    %ArrayIteratorPrototype%.next() functions to be a bit more friendly
    to optimizing compilers.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, dstence@us.ibm.com
BUG=

Committed: https://crrev.com/fdbccd64f7054f8a3328311f036e4f59a1b52131
Cr-Commit-Position: refs/heads/master@{#30575}

[dstence, 2015-09-03 18:15:37]

lgtm

[MTBrandyberry, 2015-09-03 18:16:51]

The CQ bit was checked by mbrandy@us.ibm.com

[commit-bot: I haz the power, 2015-09-03 18:17:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1325203004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1325203004/1

[commit-bot: I haz the power, 2015-09-03 18:41:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-03 18:41:47]

Patchset 1 (id:??) landed as
https://crrev.com/fdbccd64f7054f8a3328311f036e4f59a1b52131
Cr-Commit-Position: refs/heads/master@{#30575}