Allow retrieval of media device ID salt even after ResourceContext has gone away.

TBR=willchan@chromium.org
BUG=341211

Review URL: https://codereview.chromium.org/143003031

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251024 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251024
Blink roll 167046:167065

http://build.chromium.org/f/chromium/perf/dashboard/ui/changelog_blink.html?url=/trunk&range=167047:167065&mode=html
TBR=
BUG=

Review URL: https://codereview.chromium.org/162713002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251025 0039d316-1c4b-4281-b951-d872f2087c98
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251026 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251026