Network error interstitial bug fixes

+ Prevent flash of blue buttons before page content is populated
+ Correct the layout and size of the offline icon when getting a DNS_PROBE_FINISHED_NO_INTERNET error
+ Delay AudioContext initialising until required to reduce CPU usage.

BUG=417614
Committed: https://crrev.com/d0956cf3b7e8662b94e3ef26b4d685ddc6702a0a
Cr-Commit-Position: refs/heads/master@{#296801}

[edwardjung, 2014-09-25 15:21:21]

edwardjung@chromium.org changed reviewers:
+ thestig@chromium.org

[edwardjung, 2014-09-25 15:21:22]

Lei, some bug fixes to the recently updated network error interstitial page. 

Thanks.

[Lei Zhang, 2014-09-25 18:16:10]

thestig@chromium.org changed reviewers:
+ arv@chromium.org

[Lei Zhang, 2014-09-25 18:16:18]

deferring to arv@

[arv (Not doing code reviews), 2014-09-25 18:30:17]

LGTM

[Lei Zhang, 2014-09-25 18:33:42]

lgtm stamp then

[edwardjung, 2014-09-25 20:03:58]

The CQ bit was checked by edwardjung@chromium.org

[commit-bot: I haz the power, 2014-09-25 20:04:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/601523003/20001

[commit-bot: I haz the power, 2014-09-25 21:58:36]

Committed patchset #2 (id:20001) as c8d0e23739e9c151b638e7bb8557cd19c3f44f82

[commit-bot: I haz the power, 2014-09-25 21:59:19]

Patchset 2 (id:??) landed as
https://crrev.com/d0956cf3b7e8662b94e3ef26b4d685ddc6702a0a
Cr-Commit-Position: refs/heads/master@{#296801}