Return errors from the Mojo network service using an enum.

mojo/services/network/net_adapters.cc

Index: mojo/services/network/net_adapters.cc
diff --git a/mojo/services/network/net_adapters.cc b/mojo/services/network/net_adapters.cc
index 551481d38810370c9968a546fdf5492b2896ab27..e74bcc152d3c91eb44158290312444b8151b9789 100644
--- a/mojo/services/network/net_adapters.cc
+++ b/mojo/services/network/net_adapters.cc
@@ -108,8 +108,23 @@ MojoToNetIOBuffer::~MojoToNetIOBuffer() {
 // -----------------------------------------------------------------------------
 
 NetworkErrorPtr MakeNetworkError(int error_code) {
+  // The NetworkCode enum values defined in network_error.mojom should match net
+  // error codes from net/net_errors.h.
+  static_assert(NETWORK_CODE_OK == static_cast<NetworkCode>(net::OK),
+                "Network code enum mismatch.");
+  static_assert(
+      NETWORK_CODE_IO_PENDING == static_cast<NetworkCode>(net::ERR_IO_PENDING),
+      "Network code enum mismatch.");
+#define NET_ERROR(label, value) \
+  static_assert( \
+      NETWORK_CODE_ ## label == \
+          static_cast<NetworkCode>(net::ERR_ ## label), \
+      "Network code enum mismatch.");
+#include "net/base/net_error_list.h"
+#undef NET_ERROR
+
   NetworkErrorPtr error = NetworkError::New();
-  error->code = error_code;
+  error->code = static_cast<NetworkCode>(error_code);
   if (error_code <= 0)
     error->description = net::ErrorToString(error_code);
   return error.Pass();