[Turbofan] Only weaken types for Phi nodes.

[Turbofan] Only weaken types for Phi nodes.

We also need to fix the weakening to weaken unions with ranges in them.

BUG=

Committed: https://crrev.com/46d6ffeddd960db5ab1a2c2fd8a05436c734e047
Cr-Commit-Position: refs/heads/master@{#27257}

[Jarin, 2015-03-17 13:00:01]

jarin@chromium.org changed reviewers:
+ bmeurer@chromium.org

[Jarin, 2015-03-17 13:00:44]

How about this?

[Benedikt Meurer, 2015-03-18 09:22:31]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-03-18 09:22:31]

lgtm

[commit-bot: I haz the power, 2015-03-18 09:22:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1011103003/1

[commit-bot: I haz the power, 2015-03-18 09:25:46]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-18 09:26:05]

Patchset 1 (id:??) landed as
https://crrev.com/46d6ffeddd960db5ab1a2c2fd8a05436c734e047
Cr-Commit-Position: refs/heads/master@{#27257}