Gallery: Register unload handler to 'pagehide' event.

Gallery: Register unload handler to 'pagehide' event.

Previously the unload handler is assigned to window.unload, but the method is
not called in packaged apps.

BUG=441647
TEST=None

Committed: https://crrev.com/372a9183889718b7c11eb63d08841c5ca2e43ac0
Cr-Commit-Position: refs/heads/master@{#308962}

[hirono, 2014-12-18 01:46:45]

hirono@chromium.org changed reviewers:
+ yawano@chromium.org

[hirono, 2014-12-18 01:46:45]

PTAL the CL? Thanks!

[yawano, 2014-12-18 07:00:48]

On 2014/12/18 01:46:45, hirono wrote:
> PTAL the CL? Thanks!

lgtm. Thank you!

[hirono, 2014-12-18 07:03:45]

The CQ bit was checked by hirono@chromium.org

[commit-bot: I haz the power, 2014-12-18 07:04:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/816603002/1

[commit-bot: I haz the power, 2014-12-18 07:17:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-18 07:18:02]

Patchset 1 (id:??) landed as
https://crrev.com/372a9183889718b7c11eb63d08841c5ca2e43ac0
Cr-Commit-Position: refs/heads/master@{#308962}