Avoid dividing by zero with broken GetMscRate implementation.
Avoid dividing by zero with broken GetMscRate implementation.

Some versions of the X11 Intel GPU driver (11.1.*) seem to return 0 for
the numerator, causing a divide by zero.

BUG=598472

Review URL: https://codereview.chromium.org/1891543004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#387232}

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