Add support for extensions_unittests to the GN build

Add support for extensions_unittests to the GN build

* Fix dependency issues in //extensions
* Make protobuf library add the "src" directory to the compiler's include
  directory list, otherwise it tries to use /usr/include/google/protobuf
  which has incompatible headers.

BUG=455919
TEST=compiles and links in both component and non-component builds

Committed: https://crrev.com/f112ccdd476fc95addd79f7a120162d2f33c3473
Cr-Commit-Position: refs/heads/master@{#315067}

[James Cook, 2015-02-05 23:08:20]

jamescook@chromium.org changed reviewers:
+ rockot@chromium.org

[James Cook, 2015-02-05 23:08:20]

rockot, PTAL

[Ken Rockot(use gerrit already), 2015-02-05 23:32:45]

I am happy with all of this. All of this is good.

Except for the parts that are wrong.

But other than that, all of this is good.

LGTM!

[Ken Rockot(use gerrit already), 2015-02-05 23:33:33]

On 2015/02/05 23:32:45, Ken Rockot wrote:
> I am happy with all of this. All of this is good.
> 
> Except for the parts that are wrong.
> 
> But other than that, all of this is good.
> 
> LGTM!

Doh, what's up with linux_chromium_gn* - isn't that exactly what we were
testing?

[James Cook, 2015-02-06 00:52:22]

New patchsets have been uploaded after l-g-t-m from rockot@chromium.org

[James Cook, 2015-02-06 00:52:57]

rockot, please take another look

(browser_tests was directly including cast_channel/test_util.cc)

[Ken Rockot(use gerrit already), 2015-02-06 00:53:27]

lgtm for reals

[James Cook, 2015-02-06 00:58:36]

jamescook@chromium.org changed reviewers:
+ scottmg@chromium.org

[James Cook, 2015-02-06 00:58:36]

scottmg, can I get OWNERS for third_party/protobuf/BUILD.gn?  Ken and I ran this
by brettw and we think it's the right fix.

[scottmg, 2015-02-06 01:10:53]

On 2015/02/06 00:58:36, James Cook wrote:
> scottmg, can I get OWNERS for third_party/protobuf/BUILD.gn?  Ken and I ran
this
> by brettw and we think it's the right fix.

TIL: I'm in third_party/protobuf/OWNERS . Hmm.

lgtm

[James Cook, 2015-02-06 15:11:16]

The CQ bit was checked by jamescook@chromium.org

[commit-bot: I haz the power, 2015-02-06 15:12:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/889253004/10008

[commit-bot: I haz the power, 2015-02-06 15:17:52]

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

[commit-bot: I haz the power, 2015-02-06 15:17:53]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[James Cook, 2015-02-06 16:57:30]

New patchsets have been uploaded after l-g-t-m from
rockot@chromium.org,scottmg@chromium.org

[James Cook, 2015-02-06 16:58:08]

The CQ bit was checked by jamescook@chromium.org

[commit-bot: I haz the power, 2015-02-06 16:59:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/889253004/30001

[commit-bot: I haz the power, 2015-02-06 18:06:42]

Committed patchset #3 (id:30001)

[commit-bot: I haz the power, 2015-02-06 18:07:14]

Patchset 3 (id:??) landed as
https://crrev.com/f112ccdd476fc95addd79f7a120162d2f33c3473
Cr-Commit-Position: refs/heads/master@{#315067}