Reland Use CopyOnWriteBuffer instead of Buffer to avoid unnecessary copies.

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 6bff11a4b8793f7584d9b0100f352acb191572ae..d4678bae0f57ebf476f864af657de91da606e3f1 100644
--- a/webrtc/api/peerconnectioninterface_unittest.cc
+++ b/webrtc/api/peerconnectioninterface_unittest.cc
@@ -1400,7 +1400,7 @@ TEST_F(PeerConnectionInterfaceTest, TestSendBinaryOnRtpDataChannel) {
   EXPECT_EQ(DataChannelInterface::kOpen, data1->state());
   EXPECT_EQ(DataChannelInterface::kOpen, data2->state());
 
-  rtc::Buffer buffer("test", 4);
+  rtc::CopyOnWriteBuffer buffer("test", 4);
   EXPECT_FALSE(data1->Send(DataBuffer(buffer, true)));
 }