Reland Use CopyOnWriteBuffer instead of Buffer to avoid unnecessary copies.

webrtc/base/sslfingerprint.h

Index: webrtc/base/sslfingerprint.h
diff --git a/webrtc/base/sslfingerprint.h b/webrtc/base/sslfingerprint.h
index 735238dde669d0154ad9d3738e3dd30b5b12a62b..1413a4cd2722765fa8e619c63264746367b5ba84 100644
--- a/webrtc/base/sslfingerprint.h
+++ b/webrtc/base/sslfingerprint.h
@@ -14,7 +14,7 @@
 #include <string>
 
 #include "webrtc/base/basictypes.h"
-#include "webrtc/base/buffer.h"
+#include "webrtc/base/copyonwritebuffer.h"
 #include "webrtc/base/sslidentity.h"
 
 namespace rtc {
@@ -44,7 +44,7 @@ struct SSLFingerprint {
   std::string ToString();
 
   std::string algorithm;
-  rtc::Buffer digest;
+  rtc::CopyOnWriteBuffer digest;
 };
 
 }  // namespace rtc