Implement GetSystemLog on Linux platform

Implement GetSystemLog on Linux platform

BUG=chromium:715318

[nednguyen, 2017-05-05 21:02:36]

nednguyen@google.com changed reviewers:
+ kbr@chromium.org

[nednguyen, 2017-05-05 21:03:06]

Description was changed from

==========
Implement GetSystemLog on Linux platform

BUG=chromium:715318
==========

to

==========
Implement GetSystemLog on Linux platform

BUG=chromium:715318
==========

[nednguyen, 2017-05-05 21:03:06]

nednguyen@google.com changed reviewers:
+ ashleymarie@chromium.org

[nednguyen, 2017-05-05 21:03:11]

The CQ bit was checked by nednguyen@google.com to run a CQ dry run

[commit-bot: I haz the power, 2017-05-05 21:03:16]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-05 21:25:25]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-05 21:25:26]

Dry run: Try jobs failed on following builders:
  Catapult Linux Tryserver on master.tryserver.client.catapult (JOB_FAILED,
https://build.chromium.org/p/tryserver.client.catapult/builders/Catapult%20Li...)

[Ken Russell (switch to Gerrit), 2017-05-07 18:56:49]

lgtm

https://codereview.chromium.org/2869483003/diff/1/telemetry/telemetry/core/pl...
File telemetry/telemetry/core/platform_unittest.py (right):

https://codereview.chromium.org/2869483003/diff/1/telemetry/telemetry/core/pl...
telemetry/telemetry/core/platform_unittest.py:48:
@decorators.Disabled('android', 'win')
Is this Disabled attribute sufficient? It looks like GetSystemLog is implemented
only on macOS and Linux (with this CL). What about ChromeOS, for example?

Perhaps explicitly enable this test on the platforms where it's known to pass?