Fix source file read error in VEA unittest
Fix source file read error in VEA unittest

base::ReadFile always reads file from beginning.
Use base::File instead.

BUG=chrome-os-partner:41833
TEST=run video_HangoutHardwarePerf.vp8 and passed. Also check the
encoded output.

Review-Url: https://codereview.chromium.org/2032453002
Cr-Commit-Position: refs/heads/master@{#397340}
(cherry picked from commit a6bd1f748d1bbedc98527df5c9e085b62fd57223)

Review URL: https://codereview.chromium.org/2065483002 .

Cr-Commit-Position: 03d981dee550804c6934fd1a1d9cfa3c172affd3@{#332}
Cr-Branched-From: e9621a186760eb36d74098d9e33e4dd91c427b34@{#394939}

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