media: VEA unittest: make sure allocated memory is 64byte aligned
media: VEA unittest: make sure allocated memory is 64byte aligned

When running video_encode_accelerator_unittest :

../../media/gpu/video_encode_accelerator_unittest.cc:301: Failure
Value of: 0
Expected: reinterpret_cast<off_t>(&test_stream->aligned_in_file_data[0]) & 63
Which is: 32
File should be mapped at a 64 byte boundary

Also reuse base::bits::Align.

BUG=624254
TEST=video_encode_accelerator_unittest

Review-Url: https://codereview.chromium.org/2110063002
Cr-Commit-Position: refs/heads/master@{#403435}
(cherry picked from commit b79f630424367d6d65de0e7e0a8e80a823e79952)

Review URL: https://codereview.chromium.org/2135073002 .

Cr-Commit-Position: 03d981dee550804c6934fd1a1d9cfa3c172affd3@{#605}
Cr-Branched-From: e9621a186760eb36d74098d9e33e4dd91c427b34@{#394939}

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