Remove comparison operator and helper function from AstRawString interface

Remove comparison operator and helper function from AstRawString interface

These comparisons are only meant to be done by AstValueFactory itself (in
its string_table_ operations), so make the Compare() function a private
member of AstValueFactory.

All other clients of AstRawStrings should compare them by pointer value.
There were only two clients which failed to abide by this rule, one
recently-added (in ModuleDescriptor) and the other in Literal::Match
(in ast.cc, added in https://code.google.com/p/v8/source/detail?r=24396).

Committed: https://crrev.com/9b09a28d5c62a5d869f64b1d73ccece6bcdfa773
Cr-Commit-Position: refs/heads/master@{#27715}

[adamk, 2015-04-08 20:23:27]

adamk@chromium.org changed reviewers:
+ marja@chromium.org, svenpanne@chromium.org

[adamk, 2015-04-08 20:23:28]

marja, this patch is based on our recent email thread.

svenpanne, I've added you as a reviewer since you authored
https://code.google.com/p/v8/source/detail?r=24396, which added
AstRawString::operator==. Removing it and switching to pointer comparisons
doesn't break any tests, but I want to make sure I'm not missing anything.

[marja, 2015-04-09 06:55:45]

lgtm, this is good stuff and clarifies things!

(Hmm, I wasn't aware that operator== was added afterwards, I kinda assumed that
I had added it and it was needed!)

[Sven Panne, 2015-04-09 07:54:49]

LGTM, too. IIRC, my change was only shifting around things a bit to get rid of
the Isolate*.

[adamk, 2015-04-09 15:48:47]

The CQ bit was checked by adamk@chromium.org

[commit-bot: I haz the power, 2015-04-09 15:49:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1069423003/1

[commit-bot: I haz the power, 2015-04-09 19:38:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-09 19:38:50]

Patchset 1 (id:??) landed as
https://crrev.com/9b09a28d5c62a5d869f64b1d73ccece6bcdfa773
Cr-Commit-Position: refs/heads/master@{#27715}