Mark template class RefCountedObject as final.

pc/test/mock_datachannel.h

Index: pc/test/mock_datachannel.h
diff --git a/pc/test/mock_datachannel.h b/pc/test/mock_datachannel.h
index 4a77a6bf6046abe4029f47f7251e44868b7aeaad..30f0b313d098fb176db2b7d6c58b783b3e85cc24 100644
--- a/pc/test/mock_datachannel.h
+++ b/pc/test/mock_datachannel.h
@@ -16,7 +16,7 @@
 
 namespace webrtc {
 
-class MockDataChannel : public rtc::RefCountedObject<DataChannel> {
+class MockDataChannel : public DataChannel {
  public:
   MockDataChannel(int id, DataState state)
       : MockDataChannel(id, "MockDataChannel", state, "udp", 0, 0, 0, 0) {
@@ -30,8 +30,7 @@ class MockDataChannel : public rtc::RefCountedObject<DataChannel> {
       uint64_t bytes_sent,
       uint32_t messages_received,
       uint64_t bytes_received)
-      : rtc::RefCountedObject<DataChannel>(
-            nullptr, cricket::DCT_NONE, label) {
+      : DataChannel(nullptr, cricket::DCT_NONE, label) {
     EXPECT_CALL(*this, id()).WillRepeatedly(testing::Return(id));
     EXPECT_CALL(*this, state()).WillRepeatedly(testing::Return(state));
     EXPECT_CALL(*this, protocol()).WillRepeatedly(testing::Return(protocol));