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The permission checking will be done using the extension's
permissions specified in its manifest data, similar to what
is being done in ShellExtensionHostDelegate.

Also moved media_capture_util code to extensions/browser for better
code sharing and add an API for checking media access permission
for a given extension.

Bug: b/78193883
Test: Build
Change-Id: I7bd9d9a771b5a6d8ca719b5480e42f4624a1bb69
Reviewed-on: https://chromium-review.googlesource.com/1022316
Commit-Queue: Peter Qiu <zqiu@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552940}