[turbofan] Make global variable loads and stores explicit.

[turbofan] Make global variable loads and stores explicit.

This is a precursor to using specialized LoadIC and StoreIC stubs for
global variable access. It also removes the need to keep track of the
global object in the type system, hence freeing up one bit.

R=bmeurer@chromium.org

Committed: https://crrev.com/7f5a2d9ed530dddf29232f6d29ca850df1b1cf90
Cr-Commit-Position: refs/heads/master@{#29231}

[Benedikt Meurer, 2015-06-23 12:23:46]

LGTM. Thanks.

[Michael Starzinger, 2015-06-23 13:09:17]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-06-23 13:09:33]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1205473004/1

[commit-bot: I haz the power, 2015-06-23 13:34:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-23 13:34:17]

Patchset 1 (id:??) landed as
https://crrev.com/7f5a2d9ed530dddf29232f6d29ca850df1b1cf90
Cr-Commit-Position: refs/heads/master@{#29231}