Media/ should describe its decode capabilities. Embedders may
override via MediaClient. For time being, this preserves the
simple logic from content::RenderMediaClient. In the long run
it will check profiles for actual decoder support and include
android specific logic currently in MimeUtilInternal.

BUG=695264

Review-Url: https://codereview.chromium.org/2758873003
Cr-Commit-Position: refs/heads/master@{#459352}