Revert of Revert: Per navigation sticky media permissions. (https://codereview.chromi...

Revert of Revert: Per navigation sticky media permissions. (https://codereview.chromium.org/336653002/)

Reason for revert:
THis CL breaks several WebRTC bots. See e.g. http://chromegw.corp.google.com/i/internal.chromium.webrtc/builders/Win7%20Tester.

[32/32] WebRtcWebcamBrowserTests/WebRtcWebcamBrowserTest.TestAcquiringAndReacquiringWebcam/1 (TIMED OUT)
2 tests timed out:
    WebRtcWebcamBrowserTests/WebRtcWebcamBrowserTest.TestAcquiringAndReacquiringWebcam/0
    WebRtcWebcamBrowserTests/WebRtcWebcamBrowserTest.TestAcquiringAndReacquiringWebcam/1

Original issue's description:
> Revert: Per navigation sticky media permissions.
> This CL re-enables the same behavior for getUserMedia prompts as it was in M35.
> The reason for this is because there was a change of hearts at the standards level about this.
> More information in the issue.
>
> BUG=269719
> COLLABORATOR=xians
>
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=276974

TBR=xians@chromium.org,tommi@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=269719

Review URL: https://codereview.chromium.org/338753002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@277377 0039d316-1c4b-4281-b951-d872f2087c98