[telemetry] Only run reference builds on desktop.

[telemetry] Only run reference builds on desktop.

Maintain a whitelist of which browsers it makes sense to compare with --browser=reference (doesn't include system)

BUG=416705
TEST=None.
TBR=tonyg
NOTRY=True

Committed: https://crrev.com/c81f0c984d7096e8d671645d08a1844f11ad6a19
Cr-Commit-Position: refs/heads/master@{#296373}

[dtu, 2014-09-24 09:35:30]

The CQ bit was checked by dtu@chromium.org

[commit-bot: I haz the power, 2014-09-24 09:36:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/601713002/1

[commit-bot: I haz the power, 2014-09-24 09:36:35]

Committed patchset #1 (id:1) as b2d5fa84aff5ef51df53286ad33341cb17627adc

[commit-bot: I haz the power, 2014-09-24 09:37:14]

Patchset 1 (id:??) landed as
https://crrev.com/c81f0c984d7096e8d671645d08a1844f11ad6a19
Cr-Commit-Position: refs/heads/master@{#296373}

[tonyg, 2014-09-24 16:12:31]

Seems like it's a bug that we check out the linux reference build on the android
bots. Why don't we look into fixing up the DEPS file so that doesn't happen.
Then we can remove this logic and it simply won't find a reference build.