Reland "LayoutDescriptor should inherit from JSTypedArray"

Reland "LayoutDescriptor should inherit from JSTypedArray"

Original issue's description:
> LayoutDescriptor should inherit from JSTypedArray
>
> It can't just inherit from a FixedTypedArray-like type, as we soon
> assume that a FixedTypedArray-like type is always held by an
> ArrayBufferView-like type
>
> BUG=v8:3996
> R=ishell@chromium.org,verwaest@chromium.org
> LOG=n

BUG=v8:3996
R=ishell@chromium.org,verwaest@chromium.org
LOG=n

Committed: https://crrev.com/d20660e05eb9329cd7a0349b6afcbc794bc737c1
Cr-Commit-Position: refs/heads/master@{#27973}

[jochen (gone - plz use gerrit), 2015-04-21 14:24:48]

ptal

since the actual values are now in a different object pointed at by elements, we
need to check for forwarding addresses during scavange

[jochen (gone - plz use gerrit), 2015-04-21 14:25:13]

patch set #1 is the original CL, patch set #2 has the fix

[Igor Sheludko, 2015-04-21 14:27:07]

lgtm

[jochen (gone - plz use gerrit), 2015-04-21 14:30:10]

The CQ bit was checked by jochen@chromium.org

[jochen (gone - plz use gerrit), 2015-04-21 14:30:10]

The patchset sent to the CQ was uploaded after l-g-t-m from ishell@chromium.org
Link to the patchset: https://codereview.chromium.org/1094333002/#ps40001
(title: "updates")

[commit-bot: I haz the power, 2015-04-21 14:30:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1094333002/40001

[commit-bot: I haz the power, 2015-04-21 15:22:03]

Committed patchset #3 (id:40001)

[jochen (gone - plz use gerrit), 2015-04-21 15:58:02]

A revert of this CL (patchset #3 id:40001) has been created in
https://codereview.chromium.org/1080403004/ by jochen@chromium.org.

The reason for reverting is: Breaks gbemu.

[commit-bot: I haz the power, 2015-04-22 04:10:23]

Patchset 3 (id:??) landed as
https://crrev.com/d20660e05eb9329cd7a0349b6afcbc794bc737c1
Cr-Commit-Position: refs/heads/master@{#27973}