Reset manual zoom mode on navigation.

Reset manual zoom mode on navigation.

When an app/extension places a ZoomController in manual mode, it is
reasonable to expect that navigating the main frame should reset that
mode, since the app/extension will be reloaded in the process.

The root cause of this bug was the sending of a ZoomChangeEvent that
contained stale information (the old, manually managed, zoom level),
which in turn caused the zoom bubble to be displayed.

BUG=450909
Committed: https://crrev.com/96fc2e9e38a10f2bb9f12f26ac6842db71061e09
Cr-Commit-Position: refs/heads/master@{#313576}

[wjmaclean, 2015-01-28 17:37:57]

wjmaclean@chromium.org changed reviewers:
+ fsamuel@chromium.org

[wjmaclean, 2015-01-28 17:38:18]

fsamuel@ - small CL, please take a look?

[Fady Samuel, 2015-01-28 18:37:34]

lgtm

[wjmaclean, 2015-01-28 19:39:59]

The CQ bit was checked by wjmaclean@chromium.org

[commit-bot: I haz the power, 2015-01-28 19:41:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/884063004/1

[commit-bot: I haz the power, 2015-01-28 20:42:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-28 20:44:00]

Patchset 1 (id:??) landed as
https://crrev.com/96fc2e9e38a10f2bb9f12f26ac6842db71061e09
Cr-Commit-Position: refs/heads/master@{#313576}