Adding build_opus as a switch in GYP.

This is to allow not building Opus. On non-chromium non-gyp chases, one can let WebRTC depend on other Opus builds.

BUG=
R=kjellander@webrtc.org, tina.legrand@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/43739004

Cr-Commit-Position: refs/heads/master@{#8754}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8754 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/webrtc/modules/audio_coding/codecs/opus/opus.gypi b/webrtc/modules/audio_coding/codecs/opus/opus.gypi
index 48c7bdf..4ae4340 100644
--- a/webrtc/modules/audio_coding/codecs/opus/opus.gypi
+++ b/webrtc/modules/audio_coding/codecs/opus/opus.gypi
@@ -12,12 +12,7 @@
       'target_name': 'webrtc_opus',
       'type': 'static_library',
       'conditions': [
-        ['build_with_mozilla==1', {
-          # Mozilla provides its own build of the opus library.
-          'include_dirs': [
-            '$(DIST)/include/opus',
-           ]
-        }, {
+        ['build_opus==1', {
           'dependencies': [
             '<(opus_dir)/opus.gyp:opus'
           ],
@@ -30,6 +25,15 @@
               '<(opus_dir)/src/celt',
             ],
           },
+        }, {
+          'conditions': [
+            ['build_with_mozilla==1', {
+              # Mozilla provides its own build of the opus library.
+              'include_dirs': [
+                '$(DIST)/include/opus',
+              ]
+            }],
+          ],
         }],
       ],
       'dependencies': [