Webapps splashscreen: hide the splashscreen after the page has fully loaded.

Webapps splashscreen: hide the splashscreen after the page has fully loaded.

There are situations where the WebContents isn't notified of a first
visually non empty paint. In these rare situations, the splashscreen
will stay visible forever. As a safety net, the splashscreen will be
hidden when the page is fully loaded. At that point, there should have
been a first paint or it will happen at the very next layout.

The tests will be added as part of https://codereview.chromium.org/1405023002

BUG=531519, 542626
Committed: https://crrev.com/8efe0f049baac8abec82ef22b0a522fbf8da5e43
Cr-Commit-Position: refs/heads/master@{#354681}

[mlamouri (slow - plz ping), 2015-10-16 15:25:08]

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

[gone, 2015-10-16 17:03:22]

l-g-t-m.  Still waiting on Dave's comments, though.

[gone, 2015-10-16 17:10:07]

lgtm if you break out the fix for the beta branch; no need to gate a cherry-pick
on tests.

[mlamouri (slow - plz ping), 2015-10-17 12:22:29]

The CQ bit was checked by mlamouri@chromium.org

[mlamouri (slow - plz ping), 2015-10-17 12:22:29]

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/1405413002/#ps20001
(title: "rebase + no tests")

[commit-bot: I haz the power, 2015-10-17 12:22:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1405413002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1405413002/20001

[commit-bot: I haz the power, 2015-10-17 12:52:43]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-17 12:53:31]

Patchset 2 (id:??) landed as
https://crrev.com/8efe0f049baac8abec82ef22b0a522fbf8da5e43
Cr-Commit-Position: refs/heads/master@{#354681}