Add window.IN_TEST in gallery/js/background.js.

Add window.IN_TEST in gallery/js/background.js.

window.IN_TEST is not defined in gallery app. It caused a warning of closure compiler, and IN_TEST flag should be set true also in tests of gallery app.

BUG=433728
TEST=GYP_GENERATORS=ninja tools/gyp/gyp --depth . ui/file_manager/gallery/js/compiled_resources.gyp && ninja -C out/Default
out/Release/browser_tests --gtest_filter=*GalleryBrowserTest*

Committed: https://crrev.com/9965b3de0a9760e3fe23e7a8ad3888229ff29b67
Cr-Commit-Position: refs/heads/master@{#309402}

[yawano, 2014-12-22 05:47:07]

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

[yawano, 2014-12-22 05:47:07]

PTAL. Thank you!

[mtomasz, 2014-12-22 05:57:54]

lgtm

[yawano, 2014-12-22 05:58:15]

On 2014/12/22 05:57:54, mtomasz wrote:
> lgtm

Thank you!

[yawano, 2014-12-22 05:58:23]

The CQ bit was checked by yawano@chromium.org

[commit-bot: I haz the power, 2014-12-22 05:58:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/817233002/1

[commit-bot: I haz the power, 2014-12-22 06:48:30]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-22 06:50:18]

Patchset 1 (id:??) landed as
https://crrev.com/9965b3de0a9760e3fe23e7a8ad3888229ff29b67
Cr-Commit-Position: refs/heads/master@{#309402}