Memory leak fix: Deleting a factory

Also expanded some documentation.
Bug found by Valgrind bot.

BUG=
TEST=

Review URL: https://webrtc-codereview.appspot.com/507002

git-svn-id: http://webrtc.googlecode.com/svn/trunk@2080 4adac7df-926f-26a2-2b94-8c16560cd09d

src/modules/udp_transport/source/udp_transport_impl.cc

@@ -169,8 +169,9 @@ UdpTransportImpl::~UdpTransportImpl()
     delete _critFilter;
     delete _critPacketCallback;
     delete _cachLock;
-
+    delete _socket_creator;
     UdpSocketManager::Return();
+
     WEBRTC_TRACE(kTraceMemory, kTraceTransport, _id, "%s deleted",
                  __FUNCTION__);
 }

src/modules/udp_transport/source/udp_transport_impl.h

@@ -34,7 +34,8 @@ public:
     };
 
     // Constructor, only called by UdpTransport::Create and tests.
-    // The constructor takes ownership of the factory.
+    // The constructor takes ownership of the "maker",
+    // and will call Return on the socket_manager at exit.
     UdpTransportImpl(const WebRtc_Word32 id,
                      SocketFactoryInterface* maker,
                      UdpSocketManager* socket_manager);