Make *some* version of the Mac GN build work.

This gets at least a chunk of the Mac GN build working.

With a few additional fixes in other repos, we will have substantially more working, but this'll do to at least make the bots functional.

R=brettw@chromium.org
BUG=431117
Committed: https://crrev.com/cf8465db79634a28bdf66c8c518fccddf3af1ee9
Cr-Commit-Position: refs/heads/master@{#303540}

[Dirk Pranke, 2014-11-07 03:22:56]

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

[brettw, 2014-11-10 07:01:29]

lgtm

https://codereview.chromium.org/702003002/diff/180001/mojo/services/html_view...
File mojo/services/html_viewer/BUILD.gn (right):

https://codereview.chromium.org/702003002/diff/180001/mojo/services/html_view...
mojo/services/html_viewer/BUILD.gn:7: if (!is_mac) {
If the mac build sees this file at all, then that means a target in this file
was referenced, and since there are no targets here it will fail with an
unresolved target. If the build passes, it would seem that this file is never
referenced.

[Dirk Pranke, 2014-11-10 17:46:02]

https://codereview.chromium.org/702003002/diff/180001/mojo/services/html_view...
File mojo/services/html_viewer/BUILD.gn (right):

https://codereview.chromium.org/702003002/diff/180001/mojo/services/html_view...
mojo/services/html_viewer/BUILD.gn:7: if (!is_mac) {
On 2014/11/10 07:01:29, brettw wrote:
> If the mac build sees this file at all, then that means a target in this file
> was referenced, and since there are no targets here it will fail with an
> unresolved target. If the build passes, it would seem that this file is never
> referenced.

I think I may have commented this out in order to figure out which file was
referencing it, and then removed the reference (in mojo/services/BUILD.gn). 

I'll verify that's the case and revert this change if I can.

[Dirk Pranke, 2014-11-10 23:06:04]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2014-11-10 23:06:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/702003002/240001

[commit-bot: I haz the power, 2014-11-10 23:51:33]

Committed patchset #13 (id:240001)

[commit-bot: I haz the power, 2014-11-10 23:52:13]

Patchset 13 (id:??) landed as
https://crrev.com/cf8465db79634a28bdf66c8c518fccddf3af1ee9
Cr-Commit-Position: refs/heads/master@{#303540}