Update PlatformSensorAmbientLightMac constructor

Update PlatformSensorAmbientLightMac constructor

This CL removes the |type| parameter from PlatformSensorAmbientLightMac
constructor and updates the comments.

BUG=None

[juncai, 2017-05-03 01:15:41]

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

[commit-bot: I haz the power, 2017-05-03 01:16:37]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-03 01:36:46]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-03 01:36:47]

Dry run: This issue passed the CQ dry run.

[juncai, 2017-05-03 02:00:01]

juncai@chromium.org changed reviewers:
+ reillyg@chromium.org

[juncai, 2017-05-03 02:00:02]

Please take a look.

[Reilly Grant (use Gerrit), 2017-05-03 02:02:44]

lgtm

[juncai, 2017-05-03 02:56:34]

The CQ bit was checked by juncai@chromium.org

[commit-bot: I haz the power, 2017-05-03 02:56:52]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-03 03:01:42]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1493780194668200, "parent_rev":
"3b5f0a15622e338cb262a307b2f4abd2ca9689c6", "commit_rev":
"9a0ab6b7a550edad5773285f46292692e5fc6a64"}

[commit-bot: I haz the power, 2017-05-03 03:03:49]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-03 03:03:51]

Prior attempt to commit was detected, but we were not able to check whether the
issue was successfully committed. Please check Git history manually and re-check
CQ or close this issue as needed.