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This CL converts MediaMetricsProvider{Ptr, Request} in content and
media to the new Mojo type.

Bug: 955171
Change-Id: I12a9cd0c377a6081ad00f3503682d13078bc6b9b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1880990Reviewed-by: Frank Liberato <liberato@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Miyoung Shin <myid.shin@igalia.com>
Cr-Commit-Position: refs/heads/master@{#709749}