Makes NativeViewport send OnBoundsChanged() after widget available

Makes NativeViewport send OnBoundsChanged() after widget available

It was possible for us to send it before.

BUG=none
TEST=none
R=ben@chromium.org, darin@chromium.org

Committed: https://crrev.com/5b19be3a063c7dd7ab0d414030750c733e6d9c56
Cr-Commit-Position: refs/heads/master@{#297472}

[sky, 2014-09-29 17:49:16]

ben: native_viewport
darin: the rest

[darin (slow to review), 2014-09-29 23:34:06]

LGTM for mojo/public

[Ben Goodger (Google), 2014-09-30 16:37:49]

lgtm

[sky, 2014-09-30 16:39:18]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2014-09-30 16:40:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/617513003/1

[commit-bot: I haz the power, 2014-09-30 19:06:36]

Committed patchset #1 (id:1) as 4f605f2e1192452c533da7841045d184a83eb1e7

[commit-bot: I haz the power, 2014-09-30 19:07:12]

Patchset 1 (id:??) landed as
https://crrev.com/5b19be3a063c7dd7ab0d414030750c733e6d9c56
Cr-Commit-Position: refs/heads/master@{#297472}