More precise MSE fallback from WMPI to WMPA.

Pass loadType() from HTMLMediaElement through to createMediaPlayer() so
that RenderFrameImpl can use that to decide which type of player to
create.

For MSE, enable WMPI if MediaCodec is unavailable. In this case WMPA
cannot play MSE at all, but WMPI can if the video codec is VPX (or if
there is no video track).

BUG=516765

Review URL: https://codereview.chromium.org/1614583002

Cr-Commit-Position: refs/heads/master@{#371033}
12 files changed