Fix issue of localDescription and remoteDescription getter.

Source/modules/mediastream/RTCPeerConnection.idl

Index: Source/modules/mediastream/RTCPeerConnection.idl
diff --git a/Source/modules/mediastream/RTCPeerConnection.idl b/Source/modules/mediastream/RTCPeerConnection.idl
index fa5494606e720f8f19b2043bc0492e96f623dd77..f0e5a07a5727027a208ee989685b24dc08168c1f 100644
--- a/Source/modules/mediastream/RTCPeerConnection.idl
+++ b/Source/modules/mediastream/RTCPeerConnection.idl
@@ -35,16 +35,18 @@
     ConstructorCallWith=ExecutionContext,
     NoInterfaceObject,
     RaisesException=Constructor,
+    SetWrapperReferenceTo(RTCSessionDescription localDescription,
+                          RTCSessionDescription remoteDescription)
 ] interface RTCPeerConnection : EventTarget {
     [RaisesException] void createOffer(RTCSessionDescriptionCallback successCallback, [Default=Undefined] optional RTCErrorCallback failureCallback, optional Dictionary rtcOfferOptions);
 
     [RaisesException] void createAnswer(RTCSessionDescriptionCallback successCallback, [Default=Undefined] optional RTCErrorCallback failureCallback, optional Dictionary mediaConstraints);
 
     [RaisesException] void setLocalDescription(RTCSessionDescription description, [Default=Undefined] optional VoidCallback successCallback, [Default=Undefined] optional RTCErrorCallback failureCallback);
-    [RaisesException=Getter] readonly attribute RTCSessionDescription localDescription;
+    readonly attribute RTCSessionDescription localDescription;
 
     [RaisesException] void setRemoteDescription(RTCSessionDescription description, [Default=Undefined] optional VoidCallback successCallback, [Default=Undefined] optional RTCErrorCallback failureCallback);
-    [RaisesException=Getter] readonly attribute RTCSessionDescription remoteDescription;
+    readonly attribute RTCSessionDescription remoteDescription;
 
     readonly attribute DOMString signalingState;