Rewrite PeerConnection integration tests using better testing practices.

webrtc/pc/test/mockpeerconnectionobservers.h

Index: webrtc/pc/test/mockpeerconnectionobservers.h
diff --git a/webrtc/pc/test/mockpeerconnectionobservers.h b/webrtc/pc/test/mockpeerconnectionobservers.h
index bde59a8d3f03ee207137d9f68cd3051c3c2840d5..94996d004f1d8e8fc5c0d5fc26371e1b3a70a8f5 100644
--- a/webrtc/pc/test/mockpeerconnectionobservers.h
+++ b/webrtc/pc/test/mockpeerconnectionobservers.h
@@ -39,8 +39,8 @@ class MockCreateSessionDescriptionObserver
   }
   bool called() const { return called_; }
   bool result() const { return result_; }
-  SessionDescriptionInterface* release_desc() {
-    return desc_.release();
+  std::unique_ptr<SessionDescriptionInterface> MoveDescription() {
+    return std::move(desc_);
   }
 
  private: