Helpers in peer connection unit tests: Use scoped_ptr instead of raw pointers

A handful of helpers were using SessionDescriptionInterface** output
arguments to return ownership. Chenge them to either use a
rtc::scoped_ptr<SessionDescriptionInterface>* output parameter, or to
simply return a rtc::scoped_ptr<SessionDescriptionInterface>. Not
using raw pointers for things you own is good in general; it will also
be very convenient when scoped_ptr is gone, since unique_ptr doesn't
have .accept() or .use() methods.

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1798173002

Cr-Commit-Position: refs/heads/master@{#12021}
diff --git a/webrtc/api/peerconnection_unittest.cc b/webrtc/api/peerconnection_unittest.cc
index 533b9db..6400655 100644
--- a/webrtc/api/peerconnection_unittest.cc
+++ b/webrtc/api/peerconnection_unittest.cc
@@ -196,7 +196,7 @@
 
   void Negotiate(bool audio, bool video) {
     rtc::scoped_ptr<SessionDescriptionInterface> offer;
-    ASSERT_TRUE(DoCreateOffer(offer.use()));
+    ASSERT_TRUE(DoCreateOffer(&offer));
 
     if (offer->description()->GetContentByName("audio")) {
       offer->description()->GetContentByName("audio")->rejected = !audio;
@@ -831,7 +831,7 @@
         webrtc::CreateSessionDescription("offer", msg, nullptr));
     EXPECT_TRUE(DoSetRemoteDescription(desc.release()));
     rtc::scoped_ptr<SessionDescriptionInterface> answer;
-    EXPECT_TRUE(DoCreateAnswer(answer.use()));
+    EXPECT_TRUE(DoCreateAnswer(&answer));
     std::string sdp;
     EXPECT_TRUE(answer->ToString(&sdp));
     EXPECT_TRUE(DoSetLocalDescription(answer.release()));
@@ -848,7 +848,7 @@
     EXPECT_TRUE(DoSetRemoteDescription(desc.release()));
   }
 
-  bool DoCreateOfferAnswer(SessionDescriptionInterface** desc,
+  bool DoCreateOfferAnswer(rtc::scoped_ptr<SessionDescriptionInterface>* desc,
                            bool offer) {
     rtc::scoped_refptr<MockCreateSessionDescriptionObserver>
         observer(new rtc::RefCountedObject<
@@ -867,18 +867,18 @@
       }
     }
     EXPECT_EQ_WAIT(true, observer->called(), kMaxWaitMs);
-    *desc = observer->release_desc();
+    desc->reset(observer->release_desc());
     if (observer->result() && ExpectIceRestart()) {
       EXPECT_EQ(0u, (*desc)->candidates(0)->count());
     }
     return observer->result();
   }
 
-  bool DoCreateOffer(SessionDescriptionInterface** desc) {
+  bool DoCreateOffer(rtc::scoped_ptr<SessionDescriptionInterface>* desc) {
     return DoCreateOfferAnswer(desc, true);
   }
 
-  bool DoCreateAnswer(SessionDescriptionInterface** desc) {
+  bool DoCreateAnswer(rtc::scoped_ptr<SessionDescriptionInterface>* desc) {
     return DoCreateOfferAnswer(desc, false);
   }