Revert of Remove MockConstraints

Revert of Remove MockConstraints (patchset #1 id:1 of https://codereview.chromium.org/1605513002/ )

Reason for revert:
Appears to be causing fast/mediastream/RTCPeerConnection.html to fail across all bots.

Original issue's description:
> Remove MockConstraints
>
> The purpose of the MockConstraints class was to verify that only legal
> constraint names were passed. This is now done inside Blink
> in MediaConstraintsImpl.cpp, so this class isn't needed any more.
>
> BUG=543997
>
> Committed: https://crrev.com/dc42f8b18dbb9c8fec81e3b7a10ab0186ce36553
> Cr-Commit-Position: refs/heads/master@{#370219}

TBR=jochen@chromium.org,tommi@chromium.org,hta@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=543997
Committed: https://crrev.com/e0dd75ac197c5df17ebe34a5f3295ea54d9e463f
Cr-Commit-Position: refs/heads/master@{#370238}

[samli, 2016-01-20 00:25:33]

Created Revert of Remove MockConstraints

[commit-bot: I haz the power, 2016-01-20 00:27:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1608073002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1608073002/1

[commit-bot: I haz the power, 2016-01-20 00:30:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-01-20 00:31:43]

Description was changed from

==========
Revert of Remove MockConstraints (patchset #1 id:1 of
https://codereview.chromium.org/1605513002/ )

Reason for revert:
Appears to be causing fast/mediastream/RTCPeerConnection.html to fail across all
bots.

Original issue's description:
> Remove MockConstraints
> 
> The purpose of the MockConstraints class was to verify that only legal
> constraint names were passed. This is now done inside Blink
> in MediaConstraintsImpl.cpp, so this class isn't needed any more.
> 
> BUG=543997
> 
> Committed: https://crrev.com/dc42f8b18dbb9c8fec81e3b7a10ab0186ce36553
> Cr-Commit-Position: refs/heads/master@{#370219}

TBR=jochen@chromium.org,tommi@chromium.org,hta@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=543997
==========

to

==========
Revert of Remove MockConstraints (patchset #1 id:1 of
https://codereview.chromium.org/1605513002/ )

Reason for revert:
Appears to be causing fast/mediastream/RTCPeerConnection.html to fail across all
bots.

Original issue's description:
> Remove MockConstraints
>
> The purpose of the MockConstraints class was to verify that only legal
> constraint names were passed. This is now done inside Blink
> in MediaConstraintsImpl.cpp, so this class isn't needed any more.
>
> BUG=543997
>
> Committed: https://crrev.com/dc42f8b18dbb9c8fec81e3b7a10ab0186ce36553
> Cr-Commit-Position: refs/heads/master@{#370219}

TBR=jochen@chromium.org,tommi@chromium.org,hta@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=543997

Committed: https://crrev.com/e0dd75ac197c5df17ebe34a5f3295ea54d9e463f
Cr-Commit-Position: refs/heads/master@{#370238}
==========

[commit-bot: I haz the power, 2016-01-20 00:31:44]

Patchset 1 (id:??) landed as
https://crrev.com/e0dd75ac197c5df17ebe34a5f3295ea54d9e463f
Cr-Commit-Position: refs/heads/master@{#370238}

[hta - Chromium, 2016-01-21 08:43:09]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1614733002/ by hta@chromium.org.

The reason for reverting is: Re-landing with fixed tests..