Raise an exception when the wpr_archive_info isn't created.

Raise an exception when the wpr_archive_info isn't created.

This is to provide a more user friendly error. This:

  AssertionError: Pageset archive_data_file path must be specified.

instead of this:

  AttributeError: 'NoneType' object has no attribute 'AddNewTemporaryRecording'

BUG=

Committed: https://crrev.com/29846e0abbd27b05029bb3e937a6bdcbc1f31b0e
Cr-Commit-Position: refs/heads/master@{#300050}

[ariblue, 2014-10-16 23:19:29]

ariblue@google.com changed reviewers:
+ dtu@chromium.org, tonyg@chromium.org

[tonyg, 2014-10-17 01:09:17]

lgtm if you go w/ the suggestion, otherwise let's iterate

https://codereview.chromium.org/660143002/diff/20001/tools/telemetry/telemetr...
File tools/telemetry/telemetry/page/record_wpr.py (right):

https://codereview.chromium.org/660143002/diff/20001/tools/telemetry/telemetr...
tools/telemetry/telemetry/page/record_wpr.py:176: raise Exception('Pageset
archive_data_file path must be specified.')
Should this be:

assert self._page_set.wpr_archive_info, 'Pageset archive data...'

Dave knows this better than me, but I think raising a generic Exception is
usually frowned upon.

[tonyg, 2014-10-17 01:09:20]

lgtm if you go w/ the suggestion, otherwise let's iterate

[ariblue, 2014-10-17 01:59:56]

The CQ bit was checked by ariblue@google.com

[commit-bot: I haz the power, 2014-10-17 02:01:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/660143002/40001

[commit-bot: I haz the power, 2014-10-17 02:55:49]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2014-10-17 02:56:34]

Patchset 3 (id:??) landed as
https://crrev.com/29846e0abbd27b05029bb3e937a6bdcbc1f31b0e
Cr-Commit-Position: refs/heads/master@{#300050}