VideoFrame method reordering and minor cleanup

      This CL cleans up a few itches I found during
previous CLs:
- Reorders VideoFrame methods to follow declaration/style guide.
- Removes VideoFrame::PlaneAllocationSize() and
replaced its use with VideoFrame::PlaneSize().GetArea() since
clients absolutely know what they are doing and
this convenience method is thus more a burden
- Turns HashFrameForTesting() into static.
- Removes ReleaseData() and binds base::AlignedFree()
directly.

BUG=489744

Review URL: https://codereview.chromium.org/1195153003

Cr-Commit-Position: refs/heads/master@{#335701}