[turbofan] Break dependency on RegisterAllocationData from Merge.

[turbofan] Break dependency on RegisterAllocationData from Merge.

Found this while working on the unit tests for split/splinter/merge. The
dependency is unnecessary and hinders testability.

BUG=

Committed: https://crrev.com/2f27911bf53949a498f7628a6ee46bb57e323f09
Cr-Commit-Position: refs/heads/master@{#30465}

[Mircea Trofin, 2015-08-31 09:48:13]

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

[Benedikt Meurer, 2015-08-31 09:53:19]

lgtm

[Mircea Trofin, 2015-08-31 09:53:29]

The CQ bit was checked by mtrofin@chromium.org

[commit-bot: I haz the power, 2015-08-31 09:53:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1325453005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1325453005/1

[commit-bot: I haz the power, 2015-08-31 10:45:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-31 10:45:32]

Patchset 1 (id:??) landed as
https://crrev.com/2f27911bf53949a498f7628a6ee46bb57e323f09
Cr-Commit-Position: refs/heads/master@{#30465}