ZoomController: manual mode SetZoom() should early-out.

ZoomController: manual mode SetZoom() should early-out.

When used in manual mode, SetZoom() should early-out if the new zoom
level is the same as the old one in order to avoid sending unnecessary
ZoomChangedEvents.

BUG=459995
Committed: https://crrev.com/bb26a8180d84b8c156005ef515f23f0308e42aae
Cr-Commit-Position: refs/heads/master@{#317323}

[wjmaclean, 2015-02-20 13:57:29]

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

[wjmaclean, 2015-02-20 13:58:04]

fsamuel@ - tiny CL, please take a quick look?

[Fady Samuel, 2015-02-20 14:12:10]

lgtm

[wjmaclean, 2015-02-20 14:29:57]

The CQ bit was checked by wjmaclean@chromium.org

[commit-bot: I haz the power, 2015-02-20 14:30:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/942023002/1

[commit-bot: I haz the power, 2015-02-20 15:29:59]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-20 15:30:49]

Patchset 1 (id:??) landed as
https://crrev.com/bb26a8180d84b8c156005ef515f23f0308e42aae
Cr-Commit-Position: refs/heads/master@{#317323}