Add metrics for DHCP WPAD feature.

net/base/net_errors.cc

Index: net/base/net_errors.cc
diff --git a/net/base/net_errors.cc b/net/base/net_errors.cc
index 6c0e09c7f13dd06b5bc63cfd674f28bd95368523..2df61f9c639e0259d9734736f7388894a096de2a 100644
--- a/net/base/net_errors.cc
+++ b/net/base/net_errors.cc
@@ -5,8 +5,21 @@
 #include "net/base/net_errors.h"
 
 #include "base/basictypes.h"
+#include "base/metrics/histogram.h"
 #include "base/stringize_macros.h"
 
+namespace {
+
+// Get all valid error codes into an array as positive numbers, for use in the
+// |GetAllErrorCodesForUma| function below.
+#define NET_ERROR(label, value) -(value),
+const int kAllErrorCodes[] = {
+#include "net/base/net_error_list.h"
+};
+#undef NET_ERROR
+
+}  // namespace
+
 namespace net {
 
 const char kErrorDomain[] = "net";
@@ -26,4 +39,9 @@ const char* ErrorToString(int error) {
   }
 }
 
+std::vector<int> GetAllErrorCodesForUma() {
+  return base::CustomHistogram::ArrayToCustomRanges(
+      kAllErrorCodes, arraysize(kAllErrorCodes));
+}
+
 }  // namespace net