[ios] Signal load cancelled after presenting SSL interstitial.

[ios] Signal load cancelled after presenting SSL interstitial.

Without this change web/ never finishes the load after presenting an SSL
interstitial. Calling |loadCancelled| fixes the problem and it's the
same approach as done in UIWebView.

BUG=551585
Committed: https://crrev.com/4cdef8fbd9a65b15ba20d62186ce9cea8a677138
Cr-Commit-Position: refs/heads/master@{#358111}

[Eugene But (OOO till 7-30), 2015-11-05 18:55:46]

eugenebut@chromium.org changed reviewers:
+ stuartmorgan@chromium.org

[stuartmorgan, 2015-11-05 19:32:03]

lgtm

[Eugene But (OOO till 7-30), 2015-11-05 19:38:48]

The CQ bit was checked by eugenebut@chromium.org

[commit-bot: I haz the power, 2015-11-05 19:39:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1434453009/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1434453009/1

[commit-bot: I haz the power, 2015-11-05 19:52:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-05 19:53:34]

Patchset 1 (id:??) landed as
https://crrev.com/4cdef8fbd9a65b15ba20d62186ce9cea8a677138
Cr-Commit-Position: refs/heads/master@{#358111}