Cleanup: Enable 125DSFForUIScaling on by default

Cleanup: Enable 125DSFForUIScaling on by default

* Fix typo
* Introduced Scoped125DSFForUIScaling to temporarily disable it for testing.
* Make sure id isn't invalid when checking if it's internal.
 This problem exists only in unit tests, not in production.

BUG=None

Committed: https://crrev.com/6cd1ca5ee1404407c70f1941a18f0ec0a83431b7
Cr-Commit-Position: refs/heads/master@{#339822}

[oshima, 2015-07-22 00:32:54]

Patchset #2 (id:20001) has been deleted

[oshima, 2015-07-22 00:32:57]

Patchset #1 (id:1) has been deleted

[oshima, 2015-07-22 00:33:59]

oshima@chromium.org changed reviewers:
+ mukai@chromium.org

[oshima, 2015-07-22 00:34:03]

The CQ bit was checked by oshima@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-07-22 00:35:34]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1251573006/40001

[oshima, 2015-07-22 00:43:01]

The CQ bit was checked by oshima@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-07-22 00:44:12]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1251573006/60001

[Jun Mukai, 2015-07-22 00:51:11]

https://codereview.chromium.org/1251573006/diff/60001/ash/display/display_inf...
File ash/display/display_info.cc (right):

https://codereview.chromium.org/1251573006/diff/60001/ash/display/display_inf...
ash/display/display_info.cc:94: if (is_internal && device_scale_factor == 1.25f)
doesn't use_125_dsf_for_ui_scaling affect this behavior anymore?

[oshima, 2015-07-22 01:09:24]

https://codereview.chromium.org/1251573006/diff/60001/ash/display/display_inf...
File ash/display/display_info.cc (right):

https://codereview.chromium.org/1251573006/diff/60001/ash/display/display_inf...
ash/display/display_info.cc:94: if (is_internal && device_scale_factor == 1.25f)
On 2015/07/22 00:51:11, Jun Mukai wrote:
> doesn't use_125_dsf_for_ui_scaling affect this behavior anymore?

Done.

[Jun Mukai, 2015-07-22 01:15:56]

lgtm

[oshima, 2015-07-22 01:37:16]

The CQ bit was checked by oshima@chromium.org

[commit-bot: I haz the power, 2015-07-22 01:37:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1251573006/80001

[commit-bot: I haz the power, 2015-07-22 02:42:55]

Committed patchset #3 (id:80001)

[commit-bot: I haz the power, 2015-07-22 02:43:31]

Patchset 3 (id:??) landed as
https://crrev.com/6cd1ca5ee1404407c70f1941a18f0ec0a83431b7
Cr-Commit-Position: refs/heads/master@{#339822}