[stubs] Refactor StringCompareStub and use it for HStringCompareAndBranch.

[stubs] Refactor StringCompareStub and use it for HStringCompareAndBranch.

The StringCompareStub used to take its parameters on the (JavaScript)
stack, which made it impossible to use in TurboFan. Actually
StringCompareStub was currently completely unused. This changes the
calling convention to something TurboFan compatible and introduces a
CallInterfaceDescriptor for StringCompareStub. It also changes
HStringCompareAndBranch to use the StringCompareStub instead of using
the full blown CompareICStub for a stupid string comparison.

R=jarin@chromium.org

Committed: https://crrev.com/8016547c8e6fde00fff0a1791f3c83b444d8af25
Cr-Commit-Position: refs/heads/master@{#30818}

[Benedikt Meurer, 2015-09-18 08:06:20]

Hey Jaro,

This is the first cleanup step for String comparison we were talking about.
TurboFan change will be followup CL.
Please take a look.

Thanks,
Benedikt

[Jarin, 2015-09-18 08:20:26]

lgtm

[Benedikt Meurer, 2015-09-18 08:21:02]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-09-18 08:21:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1347913003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1347913003/1

[commit-bot: I haz the power, 2015-09-18 08:30:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-18 08:30:59]

Patchset 1 (id:??) landed as
https://crrev.com/8016547c8e6fde00fff0a1791f3c83b444d8af25
Cr-Commit-Position: refs/heads/master@{#30818}