Use a source_set instead of static_library for libdart_embedder_noio

Use a source_set instead of static_library for libdart_embedder_noio

Some linkers (like libtool) complain when trying to create a
static_library with no sources. A source_set communicates the same thing
to GN without upsetting the linker.

[jamesr, 2015-09-10 00:56:33]

jamesr@chromium.org changed reviewers:
+ johnmccutchan@google.com

[Cutch, 2015-09-10 14:13:13]

lgtm but this is against a git mirror

[jamesr, 2015-09-10 16:03:48]

On 2015/09/10 at 14:13:13, johnmccutchan wrote:
> lgtm but this is against a git mirror

I don't have push access anyway - could you land this for me?  ("git cl patch"
doesn't care about the base url)

[Cutch, 2015-09-10 16:32:55]

On 2015/09/10 16:03:48, jamesr wrote:
> On 2015/09/10 at 14:13:13, johnmccutchan wrote:
> > lgtm but this is against a git mirror
> 
> I don't have push access anyway - could you land this for me?  ("git cl patch"
> doesn't care about the base url)

Done here- https://codereview.chromium.org/1331193002

[jamesr, 2015-09-10 16:35:49]

On 2015/09/10 at 16:32:55, johnmccutchan wrote:
> On 2015/09/10 16:03:48, jamesr wrote:
> > On 2015/09/10 at 14:13:13, johnmccutchan wrote:
> > > lgtm but this is against a git mirror
> > 
> > I don't have push access anyway - could you land this for me?  ("git cl
patch"
> > doesn't care about the base url)
> 
> Done here- https://codereview.chromium.org/1331193002

Thanks!