Run blink unit tests on Win 64-bit bots.
Run blink unit tests on Win 64-bit bots.

Running layout tests for 64-bit Windows is apparently tricky (crbug.com/178207)
but there's no reason not to run the unit tests. Since they take only a few
seconds to complete, run them on the 64-bit Win builders.

BUG=526317

Review URL: https://codereview.chromium.org/1305253005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#346503}

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