Make the default value of rtcp-mux policy to required.

webrtc/api/peerconnectioninterface_unittest.cc

Index: webrtc/api/peerconnectioninterface_unittest.cc
diff --git a/webrtc/api/peerconnectioninterface_unittest.cc b/webrtc/api/peerconnectioninterface_unittest.cc
index 71233e06081fc5d703712aaf3b6b2bcdb3be61c9..06068fd6625cd2b70fe78087923d8049ab65880b 100644
--- a/webrtc/api/peerconnectioninterface_unittest.cc
+++ b/webrtc/api/peerconnectioninterface_unittest.cc
@@ -603,6 +603,7 @@ class PeerConnectionInterfaceTest : public testing::Test {
                        nullptr) && dtls) {
       cert_generator.reset(new FakeRTCCertificateGenerator());
     }
+    config.rtcp_mux_policy = PeerConnectionInterface::kRtcpMuxPolicyNegotiate;

[honghaiz3, 2016/06/22 16:58:44]

Is there any reason to set kRtcpMuxPolicyNegotiate here?
Do we have tests to cover the new default rtcp_mux_policy?
Seems that most other methods call this method. 

[Zhi Huang, 2016/06/22 21:41:28]

Some unit tests rely on the assumption that the policy is negotiate. But I think
it make more sense to refactoring the test rather than setting the config since
we are changing to require anyway. I will fix it in next patch.

     pc_ = pc_factory_->CreatePeerConnection(
         config, constraints, std::move(port_allocator),
         std::move(cert_generator), &observer_);