Background mode: delete redundant calls to Enable/Disable.

Background mode: delete redundant calls to Enable/Disable.

After SetEnabled it is redundant to called EnableBackgroundMode
or DisableBackgroundMode as that already happens indirectly via
OnBackgroundModeEnabledPrefChange.

BUG=402456
Committed: https://crrev.com/18c38c1699d8e00c3c3b8a94fe0f8b7f0928e3d1
Cr-Commit-Position: refs/heads/master@{#348887}

[Michael van Ouwerkerk, 2015-09-01 14:20:30]

mvanouwerkerk@chromium.org changed reviewers:
+ atwilson@chromium.org

[Michael van Ouwerkerk, 2015-09-01 14:20:31]

Hi Drew, please take a look.

[Michael van Ouwerkerk, 2015-09-15 11:01:15]

Drew: please take a look.

[Peter Beverloo, 2015-09-15 13:24:02]

peter@chromium.org changed reviewers:
+ peter@chromium.org

[Peter Beverloo, 2015-09-15 13:24:03]

lgtm

[Andrew T Wilson (Slow), 2015-09-15 14:30:10]

lgtm

[Michael van Ouwerkerk, 2015-09-15 14:34:47]

The CQ bit was checked by mvanouwerkerk@chromium.org

[commit-bot: I haz the power, 2015-09-15 14:34:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1315113005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1315113005/1

[commit-bot: I haz the power, 2015-09-15 14:56:12]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-15 14:56:48]

Patchset 1 (id:??) landed as
https://crrev.com/18c38c1699d8e00c3c3b8a94fe0f8b7f0928e3d1
Cr-Commit-Position: refs/heads/master@{#348887}

[commit-bot: I haz the power, 2015-09-23 12:44:59]

Patchset 1 (id:??) landed as
https://crrev.com/18c38c1699d8e00c3c3b8a94fe0f8b7f0928e3d1
Cr-Commit-Position: refs/heads/master@{#348887}