[SystemDisplayAPI] Observe display change on linux/win/mac as well

This API wasn't working on non chromeos platforms because
it wasn't observing the display change.

BUG=316217
TEST=install the test app attached in the bug and change the scree resolution.

Committed: https://crrev.com/31eac8332a606e63d35756ad2106d545bea90677
Cr-Commit-Position: refs/heads/master@{#295733}

[oshima, 2014-09-18 23:04:19]

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

[mlamouri (slow - plz ping), 2014-09-19 08:46:44]

Great to see my Screen Orientation changes having a positive effect on other
APIs! :)

lgtm

[oshima, 2014-09-19 14:35:44]

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

[oshima, 2014-09-19 14:35:44]

scheib@ -> owners review

[scheib, 2014-09-19 15:02:53]

lgtm

[oshima, 2014-09-19 17:16:16]

The CQ bit was checked by oshima@chromium.org

[commit-bot: I haz the power, 2014-09-19 17:17:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/581023003/20001

[commit-bot: I haz the power, 2014-09-19 18:05:26]

Committed patchset #2 (id:20001) as 7c70bcfafa3432223aafe7e265c6632d249bb3e1

[commit-bot: I haz the power, 2014-09-19 18:06:08]

Patchset 2 (id:??) landed as
https://crrev.com/31eac8332a606e63d35756ad2106d545bea90677
Cr-Commit-Position: refs/heads/master@{#295733}