[Telemetry] Helpers for optional and required external modules

[Telemetry] Helpers for optional and required external modules

BUG=437525
Committed: https://crrev.com/292f72b109d2506717cb2aaed741e1a407c6d8b0
Cr-Commit-Position: refs/heads/master@{#308367}

[mthiesse, 2014-12-12 16:08:40]

mthiesse@chromium.org changed reviewers:
+ dtu@chromium.org, flackr@chromium.org, tonyg@chromium.org

[mthiesse, 2014-12-12 16:08:40]

PTAL,

Rob suggested that I have the imports for required modules raise an error on
import, rather than putting the entire module behind an if statement, so this
patch will help make it explicitly obvious when reading the code which imports
are optional and which aren't for using a module.

[tonyg, 2014-12-12 21:51:12]

Good idea, lgtm

[dtu, 2014-12-12 23:15:41]

lgtm with one comment

https://codereview.chromium.org/804513002/diff/20001/tools/telemetry/telemetr...
File tools/telemetry/telemetry/util/external_modules.py (right):

https://codereview.chromium.org/804513002/diff/20001/tools/telemetry/telemetr...
tools/telemetry/telemetry/util/external_modules.py:54: except (ImportError,
NotImplementedError):
I think NotImplementedError should be immediately fatal - it indicates a flaw in
the code.

[mthiesse, 2014-12-15 15:49:50]

The CQ bit was checked by mthiesse@chromium.org

[commit-bot: I haz the power, 2014-12-15 15:50:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/804513002/40001

[commit-bot: I haz the power, 2014-12-15 17:51:46]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2014-12-15 17:52:32]

Patchset 3 (id:??) landed as
https://crrev.com/292f72b109d2506717cb2aaed741e1a407c6d8b0
Cr-Commit-Position: refs/heads/master@{#308367}