Reland Use CopyOnWriteBuffer instead of Buffer to avoid unnecessary copies.

webrtc/api/test/fakedatachannelprovider.h

Index: webrtc/api/test/fakedatachannelprovider.h
diff --git a/webrtc/api/test/fakedatachannelprovider.h b/webrtc/api/test/fakedatachannelprovider.h
index 7899c3150a3764a64e0e62c56e81c175fb52d313..3404ac1437ad43216f73953b661a2f3a8defe607 100644
--- a/webrtc/api/test/fakedatachannelprovider.h
+++ b/webrtc/api/test/fakedatachannelprovider.h
@@ -23,7 +23,7 @@ class FakeDataChannelProvider : public webrtc::DataChannelProviderInterface {
   virtual ~FakeDataChannelProvider() {}
 
   bool SendData(const cricket::SendDataParams& params,
-                const rtc::Buffer& payload,
+                const rtc::CopyOnWriteBuffer& payload,
                 cricket::SendDataResult* result) override {
     ASSERT(ready_to_send_ && transport_available_);
     if (send_blocked_) {