Make base::PowerMonitor work on Chrome OS.

Make base::PowerMonitor work on Chrome OS.

On Chrome OS, updates about the system power status are
received via D-Bus messages on the UI thread. Being in
base/, PowerMonitor can't depend on the code in chromeos/
that receives those messages, so make the Chrome OS code
instead notify PowerMonitor when it receives updates.

BUG=326534
Committed: https://crrev.com/07366580ce28f55f6dd242c9d79e7a1f1b3bef44
Cr-Commit-Position: refs/heads/master@{#298367}

[Daniel Erat, 2014-10-02 01:16:31]

derat@chromium.org changed reviewers:
+ brettw@chromium.org

[Daniel Erat, 2014-10-02 01:16:31]

Brett, curious about your thoughts on this approach. I've tried to summarize
things at http://crbug.com/326534.

[Daniel Erat, 2014-10-02 20:59:32]

derat@chromium.org changed reviewers:
+ willchan@chromium.org
- brettw@chromium.org

[Daniel Erat, 2014-10-02 20:59:42]

redirected to will

[willchan no longer on Chromium, 2014-10-02 22:16:07]

willchan@chromium.org changed reviewers:
+ danakj@chromium.org, thestig@chromium.org

[willchan no longer on Chromium, 2014-10-02 22:16:07]

We have new base/OWNERS! Sending this review to the new victims.

[Lei Zhang, 2014-10-06 19:09:28]

lgtm but I have a question:

https://codereview.chromium.org/622693004/diff/1/base/base.gypi
File base/base.gypi (right):

https://codereview.chromium.org/622693004/diff/1/base/base.gypi#newcode842
base/base.gypi:842: ['<(chromeos) == 1', {
In most gyp files we just write chromeos==1. Why do we have to do it in the
early phase here?

[Daniel Erat, 2014-10-06 21:44:13]

https://codereview.chromium.org/622693004/diff/1/base/base.gypi
File base/base.gypi (right):

https://codereview.chromium.org/622693004/diff/1/base/base.gypi#newcode842
base/base.gypi:842: ['<(chromeos) == 1', {
On 2014/10/06 19:09:28, Lei Zhang wrote:
> In most gyp files we just write chromeos==1. Why do we have to do it in the
> early phase here?

i tried that initially, but it produces an error saying that the chromeos
identifier is undefined:

gyp: name 'chromeos' is not defined while evaluating condition 'chromeos == 1'
in /derat/chrome/src/base/base.gyp

in the existing target_condition expressions in this file, pretty much all
user-defined variables (chromeos, desktop_linux, use_glib, os_bsd, etc.) appear
to be using the early/pre-expansion syntax.

my initial thought would be that these variables are only defined after
base.gypi is included in base.gyp, but it doesn't make sense to me why early
expansion would help then (and i get the same "not defined" error when i use
late expansion, oddly). any idea what's going on here?

[Lei Zhang, 2014-10-06 21:50:01]

On 2014/10/06 21:44:13, Daniel Erat wrote:
> https://codereview.chromium.org/622693004/diff/1/base/base.gypi
> File base/base.gypi (right):
> 
> https://codereview.chromium.org/622693004/diff/1/base/base.gypi#newcode842
> base/base.gypi:842: ['<(chromeos) == 1', {
> On 2014/10/06 19:09:28, Lei Zhang wrote:
> > In most gyp files we just write chromeos==1. Why do we have to do it in the
> > early phase here?
> 
> i tried that initially, but it produces an error saying that the chromeos
> identifier is undefined:
> 
> gyp: name 'chromeos' is not defined while evaluating condition 'chromeos == 1'
> in /derat/chrome/src/base/base.gyp
> 
> in the existing target_condition expressions in this file, pretty much all
> user-defined variables (chromeos, desktop_linux, use_glib, os_bsd, etc.)
appear
> to be using the early/pre-expansion syntax.
> 
> my initial thought would be that these variables are only defined after
> base.gypi is included in base.gyp, but it doesn't make sense to me why early
> expansion would help then (and i get the same "not defined" error when i use
> late expansion, oddly). any idea what's going on here?

In a recent-ish conversion with rsleevi, it turned out I don't fully understand
how gyp's variable expansion + scoping works. So no solid idea what's going on.
I suspect it has to do with base_nacl.gyp somehow. But your use is consistent
with the rest of the file, so I think it's fine.

[Daniel Erat, 2014-10-06 22:01:48]

The CQ bit was checked by derat@chromium.org

[commit-bot: I haz the power, 2014-10-06 22:04:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/622693004/1

[commit-bot: I haz the power, 2014-10-07 01:07:53]

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

[commit-bot: I haz the power, 2014-10-07 01:07:54]

Exceeded time limit waiting for builds to trigger.

[Daniel Erat, 2014-10-07 03:26:43]

The CQ bit was checked by derat@chromium.org

[commit-bot: I haz the power, 2014-10-07 03:29:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/622693004/1

[commit-bot: I haz the power, 2014-10-07 04:18:53]

Committed patchset #1 (id:1) as b154304a2731b7d167b700aeb91f206b4b419bc5

[commit-bot: I haz the power, 2014-10-07 04:19:58]

Patchset 1 (id:??) landed as
https://crrev.com/07366580ce28f55f6dd242c9d79e7a1f1b3bef44
Cr-Commit-Position: refs/heads/master@{#298367}