Add switch for mojo tests
Add switch for mojo tests

Hopefully this makes them start working.

BUG=594600
TEST=none
R=dpranke@chromium.org

Review URL: https://codereview.chromium.org/1887853003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#387341}

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