Fix OSR to ignore phis without merge index in loop entry.

Fix OSR to ignore phis without merge index in loop entry.

This fixes a corner case introduced by escape analysis where phis are
introduced in OSR loop entry blocks that don't have a merge index and
hence cannot contain OSR values.

R=titzer@chromium.org
TEST=mjsunit/compiler/escape-analysis

Committed: http://code.google.com/p/v8/source/detail?r=16484

[Michael Starzinger, 2013-09-02 12:43:02]

Addressed offline comments.

[titzer, 2013-09-02 16:47:33]

lgtm

[Michael Starzinger, 2013-09-02 16:52:17]

Committed patchset #2 manually as r16484 (presubmit successful).