Fix issue of localDescription and remoteDescription getter.

Source/modules/mediastream/RTCSessionDescription.h

Index: Source/modules/mediastream/RTCSessionDescription.h
diff --git a/Source/modules/mediastream/RTCSessionDescription.h b/Source/modules/mediastream/RTCSessionDescription.h
index 2ef5d77cf9e5c3273e5746f9ec1f4dbda533ac65..0d9e3ef3367d31f567a53eca88499979c496d26e 100644
--- a/Source/modules/mediastream/RTCSessionDescription.h
+++ b/Source/modules/mediastream/RTCSessionDescription.h
@@ -32,6 +32,7 @@
 #define RTCSessionDescription_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
+#include "core/dom/ActiveDOMObject.h"
 #include "public/platform/WebRTCSessionDescription.h"
 #include "wtf/Forward.h"
 
@@ -41,11 +42,14 @@ class RTCSessionDescriptionInit;
 class ScriptState;
 class ScriptValue;
 
-class RTCSessionDescription final : public GarbageCollectedFinalized<RTCSessionDescription>, public ScriptWrappable {
+class RTCSessionDescription final
+    : public GarbageCollectedFinalized<RTCSessionDescription>
+    , public ScriptWrappable
+    , public ActiveDOMObject {
     DEFINE_WRAPPERTYPEINFO();
 public:
-    static RTCSessionDescription* create(const RTCSessionDescriptionInit&);
-    static RTCSessionDescription* create(WebRTCSessionDescription);
+    static RTCSessionDescription* create(ExecutionContext*, const RTCSessionDescriptionInit&);
+    static RTCSessionDescription* create(ExecutionContext*, WebRTCSessionDescription);
 
     String type();
     void setType(const String&);
@@ -56,11 +60,16 @@ public:
     ScriptValue toJSONForBinding(ScriptState*);
 
     WebRTCSessionDescription webSessionDescription();
+    void setWebSessionDescription(WebRTCSessionDescription);
 
-    DEFINE_INLINE_TRACE() { }
+    // ActiveDOMObject
+    bool hasPendingActivity() const override;
+    void stop() override;
+
+    DECLARE_VIRTUAL_TRACE();
 
 private:
-    explicit RTCSessionDescription(WebRTCSessionDescription);
+    RTCSessionDescription(ExecutionContext*, WebRTCSessionDescription);
 
     WebRTCSessionDescription m_webSessionDescription;
 };