[Feedback] Use callbacks for FeedbackCollector and use ScreenshotTask

[Feedback] Use callbacks for FeedbackCollector and use ScreenshotTask

This CL adds support for using callbacks with the FeedbackCollector.
The FeedbackCollector now always waits for the screenshot, and waits up
to 500 ms for connectivity checks to finish. If taking the screenshot
takes a long time, the connectivity checks get more time to finish.

The callback for the FeedbackCollector is called when both these
statements are true:
- Screenshot is finished.
- Connectivity checks are finished or timeout has expired.

Additional required steps part of this CL:
- Start gathering screenshots using the ScreenshotTask.
- Update all callers of HelpAndFeedback and the FeedbackCollector.

BUG=386395
Committed: https://crrev.com/a79fb716f855029ab0f35eb11b666b3bed80fb3d
Cr-Commit-Position: refs/heads/master@{#337131}

[nyquist, 2015-06-30 21:02:57]

nyquist@chromium.org changed reviewers:
+ dfalcantara@chromium.org

[nyquist, 2015-06-30 21:02:57]

dfalcantara: PTAL

[gone, 2015-07-01 18:50:41]

lgtm

[nyquist, 2015-07-01 21:27:04]

The CQ bit was checked by nyquist@chromium.org

[nyquist, 2015-07-01 21:27:04]

The patchset sent to the CQ was uploaded after l-g-t-m from
dfalcantara@chromium.org
Link to the patchset: https://codereview.chromium.org/1222453002/#ps40001
(title: "Merged in parent branch and changed CONNECTIVITY_CHECK_TIMEOUT_MS back
to 5000")

[commit-bot: I haz the power, 2015-07-01 21:27:37]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1222453002/40001

[commit-bot: I haz the power, 2015-07-01 21:29:53]

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

[commit-bot: I haz the power, 2015-07-01 21:29:54]

Exceeded global retry quota

[nyquist, 2015-07-01 21:33:20]

The CQ bit was checked by nyquist@chromium.org

[commit-bot: I haz the power, 2015-07-01 21:34:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1222453002/40001

[commit-bot: I haz the power, 2015-07-01 21:38:03]

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

[commit-bot: I haz the power, 2015-07-01 21:38:04]

Try jobs failed on following builders:
  mac_chromium_compile_dbg_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)

[nyquist, 2015-07-01 21:51:41]

The CQ bit was checked by nyquist@chromium.org

[commit-bot: I haz the power, 2015-07-01 21:52:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1222453002/40001

[commit-bot: I haz the power, 2015-07-01 21:55:37]

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

[commit-bot: I haz the power, 2015-07-01 21:55:38]

Exceeded global retry quota

[nyquist, 2015-07-01 22:20:59]

The CQ bit was checked by nyquist@chromium.org

[nyquist, 2015-07-01 22:20:59]

The patchset sent to the CQ was uploaded after l-g-t-m from
dfalcantara@chromium.org
Link to the patchset: https://codereview.chromium.org/1222453002/#ps60001
(title: "Squashed branch")

[commit-bot: I haz the power, 2015-07-01 22:22:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1222453002/60001

[commit-bot: I haz the power, 2015-07-01 23:05:09]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-07-01 23:07:09]

Patchset 4 (id:??) landed as
https://crrev.com/a79fb716f855029ab0f35eb11b666b3bed80fb3d
Cr-Commit-Position: refs/heads/master@{#337131}