Fix issue of localDescription and remoteDescription getter.

Source/modules/mediastream/RTCPeerConnection.cpp

Index: Source/modules/mediastream/RTCPeerConnection.cpp
diff --git a/Source/modules/mediastream/RTCPeerConnection.cpp b/Source/modules/mediastream/RTCPeerConnection.cpp
index 51a5d99241a3b761e296aeab803183121f94da90..bf4c52ca6f26eab85fddd3eb3c150b62a94b4c18 100644
--- a/Source/modules/mediastream/RTCPeerConnection.cpp
+++ b/Source/modules/mediastream/RTCPeerConnection.cpp
@@ -275,6 +275,8 @@ RTCPeerConnection::RTCPeerConnection(ExecutionContext* context, RTCConfiguration
         exceptionState.throwDOMException(NotSupportedError, "Failed to initialize native PeerConnection.");
         return;
     }
+    m_localDescription = RTCSessionDescription::create(context, m_peerHandler->localDescription());
+    m_remoteDescription = RTCSessionDescription::create(context, m_peerHandler->remoteDescription());
 }
 
 RTCPeerConnection::~RTCPeerConnection()
@@ -342,8 +344,8 @@ RTCSessionDescription* RTCPeerConnection::localDescription(ExceptionState& excep
     WebRTCSessionDescription webSessionDescription = m_peerHandler->localDescription();
     if (webSessionDescription.isNull())
         return nullptr;
-
-    return RTCSessionDescription::create(webSessionDescription);
+    m_localDescription->setWebSessionDescription(webSessionDescription);

[Jens Widell, 2015/04/28 10:59:22]

I think the semantics might be somewhat incorrect here (and in
setLocalDescription() + same for remote).

I don't know what might make the description change (since I don't know WebRTC
at all) but if it were to change, it seems more reasonable to return a new
RTCSessionDescription object, instead of mutating the one we have, and might
have returned earlier.

The spec definitely says to return the last description successfully via
setLocalDescription(), which implies that setLocalDescription() should make this
setter later return a different object. That is, that setLocalDescription()
should simply store the description argument in m_localDescription so that we
can return it later.

And then we should perhaps have an update mechanism here so that if we have an
existing description in m_localDescription but what
m_peerHandler->localDescription() returns doesn't match it, that we create a new
RTCSessionDescription object with that information and store it in
m_localDescription.

This is all somewhat complicated though by the fact that RTCSessionDescription
objects aren't immutable, meaning whatever description we return to the script
(or that a script sets via setLocalDescription()) could later be modified
directly by the script, which the specification doesn't mention (or at least not
where I'd expect to find it mentioned.)

+    return m_localDescription;
 }
 
 void RTCPeerConnection::setRemoteDescription(RTCSessionDescription* sessionDescription, VoidCallback* successCallback, RTCErrorCallback* errorCallback, ExceptionState& exceptionState)
@@ -365,8 +367,9 @@ RTCSessionDescription* RTCPeerConnection::remoteDescription(ExceptionState& exce
     WebRTCSessionDescription webSessionDescription = m_peerHandler->remoteDescription();
     if (webSessionDescription.isNull())
         return nullptr;
+    m_remoteDescription->setWebSessionDescription(webSessionDescription);
 
-    return RTCSessionDescription::create(webSessionDescription);
+    return m_remoteDescription;
 }
 
 void RTCPeerConnection::updateIce(const Dictionary& rtcConfiguration, const Dictionary& mediaConstraints, ExceptionState& exceptionState)
@@ -762,6 +765,9 @@ void RTCPeerConnection::stop()
 
     m_dispatchScheduledEventRunner.stop();
 
+    m_localDescription->stop();
+    m_remoteDescription->stop();
+
     m_peerHandler.clear();
 }
 
@@ -824,6 +830,8 @@ DEFINE_TRACE(RTCPeerConnection)
     visitor->trace(m_localStreams);
     visitor->trace(m_remoteStreams);
     visitor->trace(m_dataChannels);
+    visitor->trace(m_localDescription);
+    visitor->trace(m_remoteDescription);
 #if ENABLE(OILPAN)
     visitor->trace(m_scheduledEvents);
 #endif