Move MediaDevices C++ and Mojo interfaces to blink/public/common and blink/public/mojom

The Mojo interface was defined in public/platform/ and the C++ interface was defined in
content/common.

This is part of onion souping the mediastream module.

Bug: 704136
Change-Id: I06cb202e791e445779b533ecc4896d086638300e
Reviewed-on: https://chromium-review.googlesource.com/c/1405314
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Reviewed-by: Chris Palmer <palmer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#623218}
56 files changed