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We should not end up in the default implementation and want to track if this happens.

* Add new media stream result, "not supported".
* Add an error log in RenderFrameHostDelegate and WebContentsDelegate default implementations of the above functions and in Request... also use the new result.

BUG=416233
NOTRY=true

Review URL: https://codereview.chromium.org/584383002

Cr-Commit-Position: refs/heads/master@{#296779}