Make skydb chromoting aware

Presumably we should push this logic down into mojo
instead of hacking around this at the script level.

But at least this makes skydb work better for now.

R=ojan@chromium.org

Review URL: https://codereview.chromium.org/743603004

sky/tools/skydb

diff --git a/sky/tools/skydb b/sky/tools/skydb
index bf1e2a1..e834f68 100755
--- a/sky/tools/skydb
+++ b/sky/tools/skydb
@@ -58,12 +58,16 @@
             self._sky_server = subprocess.Popen(server_command)
         return 'http://localhost:%s/%s' % (HTTP_PORT, relative_path)
 
+    def _in_chromoting(self):
+        return os.environ.get('CHROME_REMOTE_DESKTOP_SESSION', False)
+
     def main(self):
         logging.basicConfig(level=logging.INFO)
 
         parser = argparse.ArgumentParser(description='Sky launcher/debugger')
         parser.add_argument('--gdb', action='store_true')
-        parser.add_argument('--use-osmesa', action='store_true')
+        parser.add_argument('--use-osmesa', action='store_true',
+            default=self._in_chromoting())
         parser.add_argument('url', nargs='?', type=str)
         args = parser.parse_args()