Refactor (simplify) creation of VideoDecodeStatsReporter

VideoDecodeStatsReporter has a few constant properties set during
construction (profile, natural_size, and soon, CdmConfig data). This CL
moves from a model of observing changes internally to instead making them
immutable. Destruction of the stats reporter will tear down the Mojo pipe
and finalize stats it may have recorded. This simplifies the logic a
great deal. Eventually fps will also be detected externally and passed in
this way.

Bug: 907909
Change-Id: If0b48d03fad9cad6427dfac4e8e3b5f54bf7e32a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1536612
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#643656}
5 files changed