[turbofan] Add support for transitioning stores to double fields.

[turbofan] Add support for transitioning stores to double fields.

This introduces an AllocateMutableHeapNumberStub for the boxed double
field case, where we need to allocate a box in case of a transitioning
store first. We cannot use our inline allocations for this currently,
because mutable HeapNumber objects have certain alignment constraints,
and I don't want to mess up Allocate/AllocateInNewSpace eagerly.

Also refactor the PropertyAccessInfoFactory slightly to split the long
methods into simpler parts.

R=jarin@chromium.org
BUG=v8:4470
LOG=n

Committed: https://crrev.com/17a651917ae2aa54335dc76d6bcf69d1d86711ec
Cr-Commit-Position: refs/heads/master@{#31695}

[Benedikt Meurer, 2015-10-30 14:38:34]

Hey Jaro,

Here's the last missing piece for transitioning field stores. Also please
appreciate the cleanup. :-)
Please take a look.

Thanks,
Benedikt

[Jarin, 2015-10-30 15:01:45]

nice (well, at least the bits I understand look nice :-)). lgtm.

[Benedikt Meurer, 2015-10-30 15:02:44]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-10-30 15:02:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1419173007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1419173007/1

[commit-bot: I haz the power, 2015-10-30 16:11:59]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-30 16:12:24]

Patchset 1 (id:??) landed as
https://crrev.com/17a651917ae2aa54335dc76d6bcf69d1d86711ec
Cr-Commit-Position: refs/heads/master@{#31695}