Add constructors for WebAudio nodes

third_party/WebKit/Source/modules/webaudio/PannerNode.idl

Index: third_party/WebKit/Source/modules/webaudio/PannerNode.idl
diff --git a/third_party/WebKit/Source/modules/webaudio/PannerNode.idl b/third_party/WebKit/Source/modules/webaudio/PannerNode.idl
index a3ddf5ca6b2ec75034af9cc7a784a057c6f113e8..bcc36ccea0512b6bb5eda391276b970e72b636c5 100644
--- a/third_party/WebKit/Source/modules/webaudio/PannerNode.idl
+++ b/third_party/WebKit/Source/modules/webaudio/PannerNode.idl
@@ -22,6 +22,7 @@
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+// See https://webaudio.github.io/web-audio-api/#the-pannernode-interface
 enum PanningModelType {
     "equalpower",
     "HRTF"
@@ -34,7 +35,8 @@ enum DistanceModelType {
 };
 
 [
-    NoInterfaceObject,
+    Constructor(BaseAudioContext context, optional PannerOptions options),
+    RaisesException=Constructor,
 ] interface PannerNode : AudioNode {
     // Default model for stereo is equalpower.
     attribute PanningModelType panningModel;