GN: Add assert that //components/exo is referenced only on supported platforms

GN: Add assert that //components/exo is referenced only on supported platforms

BUG=

[agrieve, 2015-12-23 19:56:52]

agrieve@chromium.org changed reviewers:
+ reveman@chromium.org

[agrieve, 2015-12-23 19:56:52]

☃

[reveman, 2015-12-24 00:24:25]

what are the platforms for which this code is not supported and why not? do we
have a similar assert for src/ash/? this code should build anywhere ash builds,
I think.

[agrieve, 2015-12-28 19:24:52]

On 2015/12/24 00:24:25, reveman wrote:
> what are the platforms for which this code is not supported and why not? do we
> have a similar assert for src/ash/? this code should build anywhere ash
builds,
> I think.

Switched to asserting enable_wayland_server, which matches the actual inclusion
condition in chrome/browser/BUILD.gn

The corresponding ash change is here:
https://codereview.chromium.org/1542633006/

[reveman, 2015-12-28 21:12:57]

On 2015/12/28 at 19:24:52, agrieve wrote:
> On 2015/12/24 00:24:25, reveman wrote:
> > what are the platforms for which this code is not supported and why not? do
we
> > have a similar assert for src/ash/? this code should build anywhere ash
builds,
> > I think.
> 
> Switched to asserting enable_wayland_server, which matches the actual
inclusion condition in chrome/browser/BUILD.gn

That's not right. You should be able to build exo without wayland server
support.

> 
> The corresponding ash change is here:
https://codereview.chromium.org/1542633006/

[agrieve, 2015-12-28 21:54:17]

On 2015/12/28 21:12:57, reveman wrote:
> On 2015/12/28 at 19:24:52, agrieve wrote:
> > On 2015/12/24 00:24:25, reveman wrote:
> > > what are the platforms for which this code is not supported and why not?
do
> we
> > > have a similar assert for src/ash/? this code should build anywhere ash
> builds,
> > > I think.
> > 
> > Switched to asserting enable_wayland_server, which matches the actual
> inclusion condition in chrome/browser/BUILD.gn
> 
> That's not right. You should be able to build exo without wayland server
> support.
> 
> > 
> > The corresponding ash change is here:
> https://codereview.chromium.org/1542633006/

My goal for this is to ensure exo is not pulled in for android, but I think it
makes more sense to use a whitelist rather than a blacklist. Do you know what
the whitelist should contain?

is_linux || is_win?

[reveman, 2015-12-29 08:15:05]

On 2015/12/28 at 21:54:17, agrieve wrote:
> On 2015/12/28 21:12:57, reveman wrote:
> > On 2015/12/28 at 19:24:52, agrieve wrote:
> > > On 2015/12/24 00:24:25, reveman wrote:
> > > > what are the platforms for which this code is not supported and why not?
do
> > we
> > > > have a similar assert for src/ash/? this code should build anywhere ash
> > builds,
> > > > I think.
> > > 
> > > Switched to asserting enable_wayland_server, which matches the actual
> > inclusion condition in chrome/browser/BUILD.gn
> > 
> > That's not right. You should be able to build exo without wayland server
> > support.
> > 
> > > 
> > > The corresponding ash change is here:
> > https://codereview.chromium.org/1542633006/
> 
> My goal for this is to ensure exo is not pulled in for android, but I think it
makes more sense to use a whitelist rather than a blacklist. Do you know what
the whitelist should contain?
> 
> is_linux || is_win?

Why do we want artificial constraints for where this can be built?  We should be
able to build and run the exo/ unittests on android if we want to. If this is
currently being built somewhere where we don't want it to be built then that's a
configuration problem at a different level. Nothing wrong with building for
android from the src/exo/ pov.