A lightweight WebP parser that validates that a given data stream
encodes a lossy WebP image by following the WebP Container Specification
found at: https://devsite.googleplex.com/speed/webp/docs/riff_container
After format validation, the parser uses the Vp8Parser to parse the VP8
key frame and returns a Vp8FrameHeader when parsing succeeds.
Note: This parser only supports lossy WebP formats.

There are two reasons in favor of rolling out a new lightweight WebP
parser (instead of using libwebp):
1) It's going to be used both by the render and gpu processes. Avoiding
a third-party lib is preferable.
2) the Vp8Parser was written to fit the VA-API better, i.e. it produces
objects that can be fed into the VA-API with minimum processing.

This change also moves the VP8 parser from //media/filters to
//media/parser.

Bug: 877694
Test: WebpParserTest.*
Change-Id: Ia553bc320cf0c136a859d24a4422e2bcc6e9c2c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1617637
Commit-Queue: Gil Dekel <gildekel@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Andres Calderon Jaramillo <andrescj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663975}