Use CertificateReportSender error callback to record HPKP UMA metrics

net/http/transport_security_state.h

Index: net/http/transport_security_state.h
diff --git a/net/http/transport_security_state.h b/net/http/transport_security_state.h
index a35e18595db0ddf982c6d963c959b0bbcdf5faf5..0f9548fcfa9217fd7317167087269d6c75fd4cc2 100644
--- a/net/http/transport_security_state.h
+++ b/net/http/transport_security_state.h
@@ -12,6 +12,7 @@
 #include <utility>
 #include <vector>
 
+#include "base/callback.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/threading/non_thread_safe.h"
@@ -203,6 +204,10 @@ class NET_EXPORT TransportSecurityState
     // Sends the given serialized |report| to |report_uri|.
     virtual void Send(const GURL& report_uri, const std::string& report) = 0;
 
+    // Sets a callback to be called when report sending fails.
+    virtual void SetErrorCallback(
+        const base::Callback<void(GURL, int)>& error_callback) = 0;

[eroman, 2016/04/02 01:55:25]

why not a const GURL?

[estark, 2016/04/05 00:57:29]

Done.

+
    protected:
     virtual ~ReportSender() {}
   };