Add metrics for DHCP WPAD feature.

net/base/net_errors.h

Index: net/base/net_errors.h
diff --git a/net/base/net_errors.h b/net/base/net_errors.h
index 5ae8b2716b721a689eccfdb51e793a9149564a05..02451690b56ca7378f75bc9ba4254c58440f8dbc 100644
--- a/net/base/net_errors.h
+++ b/net/base/net_errors.h
@@ -6,6 +6,8 @@
 #define NET_BASE_NET_ERRORS_H__
 #pragma once
 
+#include <vector>
+
 #include "base/basictypes.h"
 
 namespace net {
@@ -39,6 +41,15 @@ inline bool IsCertificateError(int error) {
 // Map system error code to Error.
 Error MapSystemError(int os_error);
 
+// Returns a list of all the possible net error codes (not counting OK). This
+// is intended for use with UMA histograms that are reporting the result of
+// an action that is represented as a net error code.
+//
+// Note that the error codes are all positive (since histograms expect positive
+// sample values). Also note that a guard bucket is created after any valid
+// error code that is not followed immediately by a valid error code.
+std::vector<int> GetAllErrorCodesForUma();
+
 }  // namespace net
 
 #endif  // NET_BASE_NET_ERRORS_H__