Reland of permissions: remove duplicates from request multiple at the Blink level

Reland of permissions: remove duplicates from request multiple at the Blink level (patchset #1 id:1 of https://codereview.chromium.org/1381353002/ )

Reason for revert:
Depending CL has relanded.

Original issue's description:
> Revert of permissions: remove duplicates from request multiple at the Blink level (patchset #4 id:60001 of https://codereview.chromium.org/1360023005/ )
>
> Reason for revert:
> BUG=538717
>
> Original issue's description:
> > permissions: remove duplicates from request multiple at the Blink level
> >
> > Propogating this information all the way to PermissionManager so it can be handled there
> > seems to be a waste of time and memory. It also adds a bunch of complexity to
> > all PermissionManager implementations.
> >
> > Instead of this, handle all duplication at the Blink level so that chrome
> > can focus on handling requests.
> >
> > BUG=516626
> >
> > Committed: https://crrev.com/b3d2e697dc79112379f96f0f34cf26b83227a737
> > Cr-Commit-Position: refs/heads/master@{#352072}
>
> TBR=mlamouri@chromium.org,lalitm@google.com
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=516626
>
> Committed: https://crrev.com/274f94ac26b2c789770e9280295a4f7dc71a8be0
> Cr-Commit-Position: refs/heads/master@{#352113}

TBR=lalitm@google.com,dmurph@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=538717
Committed: https://crrev.com/658cc2178366755f9d54267e03a241f721be1873
Cr-Commit-Position: refs/heads/master@{#352256}

[mlamouri (slow - plz ping), 2015-10-03 14:53:02]

Created Reland of permissions: remove duplicates from request multiple at the
Blink level

[commit-bot: I haz the power, 2015-10-03 14:53:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1381423002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1381423002/1

[commit-bot: I haz the power, 2015-10-03 14:53:37]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-03 14:54:23]

Patchset 1 (id:??) landed as
https://crrev.com/658cc2178366755f9d54267e03a241f721be1873
Cr-Commit-Position: refs/heads/master@{#352256}