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Previously it didn't, and perhaps there was no need for
it to, but it seems like NaCl has a need. Specifically,
NaCl has two targets A and B with both run fine on their
own, but A can delete the output of B, and so needs to run
before B.

R=brettw@chromium.org
BUG=428576

Review URL: https://codereview.chromium.org/693443002

Cr-Commit-Position: refs/heads/master@{#302342}