Revert of Revert of Add explicit support for discovering the GpuProcess to Telemetry's 'Model'.

Revert of Revert of Add explicit support for discovering the GpuProcess to Telemetry's 'Model'. (patchset #1 id:1 of https://codereview.chromium.org/819643006/)

Reason for revert:
Per discussion with owner (skyostil@) and analysis of subsequent flakes that continued to demonstrate the reported problem after the revert, we've concluded that the original change is not responsible for the flakes. Reverting the revert.

Original issue's description:
> Revert of Add explicit support for discovering the GpuProcess to Telemetry's 'Model'. (patchset #1 id:1 of https://codereview.chromium.org/816833006/)
>
> Reason for revert:
> Since this CL landed, we've been seeing flakes in Mac 10.9 telemetry_unittests. It's not clear that this CL is responsible, but the timing is suspicious.
>
> Recent 10.9 failures:
> https://build.chromium.org/p/chromium.mac/builders/Mac10.9%20Tests%20(dbg)
>
> Detailed log: https://build.chromium.org/p/chromium.mac/builders/Mac10.9%20Tests%20%28dbg%29/builds/1965/steps/telemetry_unittests/logs/stdio
>
> Original issue's description:
> > Add explicit support for discovering the GpuProcess to Telemetry's 'Model'.
> >
> > BUG=
> >
> > Committed: https://crrev.com/f6ade006723de6a100b6dd6b545cb5916b197925
> > Cr-Commit-Position: refs/heads/master@{#311486}
>
> TBR=skyostil@chromium.org,tonyg@chromium.org,andrewhayden@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=
>
> Committed: https://crrev.com/8bb2a47135a731b12116feb832a9dc6433729fa2
> Cr-Commit-Position: refs/heads/master@{#311592}

TBR=skyostil@chromium.org,tonyg@chromium.org,rch@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=

Committed: https://crrev.com/485738423ed010285477392c73c588af9cb5c663
Cr-Commit-Position: refs/heads/master@{#311647}

[Andrew Hayden (chromium.org), 2015-01-15 10:56:58]

Created Revert of Revert of Add explicit support for discovering the GpuProcess
to Telemetry's 'Model'.

[commit-bot: I haz the power, 2015-01-15 10:57:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/847433005/1

[commit-bot: I haz the power, 2015-01-15 10:58:24]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-15 10:59:14]

Patchset 1 (id:??) landed as
https://crrev.com/485738423ed010285477392c73c588af9cb5c663
Cr-Commit-Position: refs/heads/master@{#311647}

[Sami, 2015-01-15 11:03:24]

On 2015/01/15 10:59:14, I haz the power (commit-bot) wrote:
> Patchset 1 (id:??) landed as
> https://crrev.com/485738423ed010285477392c73c588af9cb5c663
> Cr-Commit-Position: refs/heads/master@{#311647}

lgtm.