Add filter function to gpu_times.

Add filter function to gpu_times.

In order to prepare for future changes where additional metrics
will be added to the TBM module, I have also preemptively added a
filter function which filters out values relating to gpu_times.

R=nednguyen@chromium.org
BUG=455292, 453131
Committed: https://crrev.com/7984b4ad04d0e3f9e4d4881056eec9721fd53f5d
Cr-Commit-Position: refs/heads/master@{#318154}

[David Yen, 2015-02-25 23:10:17]

dyen@chromium.org changed reviewers:
+ nednguyen@google.com
- nednguyen@chromium.org

[David Yen, 2015-02-25 23:10:18]

Partial revert of the previous CL revert, keep tests disabled.

[nednguyen, 2015-02-25 23:29:13]

lgtm

[David Yen, 2015-02-25 23:30:16]

The CQ bit was checked by dyen@chromium.org

[commit-bot: I haz the power, 2015-02-25 23:31:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/959983002/1

[commit-bot: I haz the power, 2015-02-26 00:19:39]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-26 00:20:13]

Patchset 1 (id:??) landed as
https://crrev.com/7984b4ad04d0e3f9e4d4881056eec9721fd53f5d
Cr-Commit-Position: refs/heads/master@{#318154}