Remove an expectation for an exception from CrossOriginXHRBackgroundPage test

Remove an expectation for an exception from CrossOriginXHRBackgroundPage test

XHR stops throwing NetworkError exceptions from
https://codereview.chromium.org/1060113004/

Prepare for it by removing chrome.test.fail() call but keeping the
expectation set for the error event.

After landing the Blink side patch, remove the try-catch.

BUG=479484
R=yhirano

Committed: https://crrev.com/5ef30a1f6ebdf7a7ffc1e48eb843814987866246
Cr-Commit-Position: refs/heads/master@{#339828}

[tyoshino (SeeGerritForStatus), 2015-07-21 06:41:55]

tyoshino@chromium.org changed reviewers:
+ yhirano@chromium.org

[yhirano, 2015-07-21 06:47:53]

lgtm

[tyoshino (SeeGerritForStatus), 2015-07-21 07:41:53]

The CQ bit was checked by tyoshino@chromium.org

[commit-bot: I haz the power, 2015-07-21 07:41:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1238313003/1

[commit-bot: I haz the power, 2015-07-21 08:19:12]

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

[commit-bot: I haz the power, 2015-07-21 08:19:13]

Try jobs failed on following builders:
  linux_chromium_asan_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[tyoshino (SeeGerritForStatus), 2015-07-21 08:35:16]

yhirano: PTAL. We need two steps. Changed this CL to just remove the
chrome.test.fail() call.

[yhirano, 2015-07-21 08:36:02]

lgtm

[tyoshino (SeeGerritForStatus), 2015-07-21 08:36:41]

The CQ bit was checked by tyoshino@chromium.org

[commit-bot: I haz the power, 2015-07-21 08:36:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1238313003/20001

[commit-bot: I haz the power, 2015-07-21 09:58:12]

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

[commit-bot: I haz the power, 2015-07-21 09:58:13]

Try jobs failed on following builders:
  win_chromium_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[tyoshino (SeeGerritForStatus), 2015-07-22 02:27:34]

The CQ bit was checked by tyoshino@chromium.org

[commit-bot: I haz the power, 2015-07-22 02:27:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1238313003/20001

[commit-bot: I haz the power, 2015-07-22 03:12:39]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-07-22 03:13:11]

Patchset 2 (id:??) landed as
https://crrev.com/5ef30a1f6ebdf7a7ffc1e48eb843814987866246
Cr-Commit-Position: refs/heads/master@{#339828}