Reland of Provide the DeviceManager service to the renderer directly, no app.

Reland of Provide the DeviceManager service to the renderer directly, no app. (patchset #1 id:1 of https://codereview.chromium.org/1382383002/ )

Reason for revert:
Revert the revert, since it doesn't apply cleanly (despite passing the CQ)  (sigh)

Original issue's description:
> Revert of Provide the DeviceManager service to the renderer directly, no app. (patchset #5 id:80001 of https://codereview.chromium.org/1371793004/ )
>
> Reason for revert:
> It is causing a number of layout tests to fail with error:
>
> 01:16:18.824 21620   [4:4:1005/011618:1968830910:ERROR:web_usb_client_impl.cc(72)] Device manager connection failed.
>
> See for example:
> http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.6/builds/45170/steps/webkit_tests/logs/stdio
>
> Original issue's description:
> > Provide the DeviceManager service to the renderer directly, no app.
> >
> > The Mojo app model forces us to create a new thread on which to run the
> > device manager. Inside Chrome this then means that we have to post tasks
> > to the UI thread in order to use the UsbService instance it is
> > implemented with. This patch removes the devices app from Chrome,
> > instead registering a factory function for DeviceManagers directly with
> > the RenderFrameHost. DeviceManagerImpl can then live on the UI thread
> > which greatly simplfies its implementation. Otherwise we would have to
> > implement similar thread hopping in DeviceImpl and that would be a lot
> > of unnecessary code.
> >
> > Committed: https://crrev.com/869af1c5170c48b8987b7ce4e2c70c9b37f9beb7
> > Cr-Commit-Position: refs/heads/master@{#352222}
>
> TBR=rockot@chromium.org,thestig@chromium.org,jam@chromium.org,reillyg@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
>
> Committed: https://crrev.com/66407392ea95965f34b9c69993d0da3a674ca60b
> Cr-Commit-Position: refs/heads/master@{#352312}

TBR=rockot@chromium.org,thestig@chromium.org,jam@chromium.org,reillyg@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/61535c70cc8d3617f6112079545ac58e21599ed2
Cr-Commit-Position: refs/heads/master@{#352315}

[Finnur, 2015-10-05 11:08:59]

Created Reland of Provide the DeviceManager service to the renderer directly, no
app.

[commit-bot: I haz the power, 2015-10-05 11:09:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1387823002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1387823002/1

[commit-bot: I haz the power, 2015-10-05 11:10:13]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-05 11:10:52]

Patchset 1 (id:??) landed as
https://crrev.com/61535c70cc8d3617f6112079545ac58e21599ed2
Cr-Commit-Position: refs/heads/master@{#352315}