Add runtime and native entry tags

runtime/bin/io_natives.cc

Index: runtime/bin/io_natives.cc
diff --git a/runtime/bin/io_natives.cc b/runtime/bin/io_natives.cc
index 86d7c2d8f22e121e93759de0143acdc4e89c6d63..e10bdd4557500d61e079c9c71358b5314de283aa 100644
--- a/runtime/bin/io_natives.cc
+++ b/runtime/bin/io_natives.cc
@@ -124,5 +124,17 @@ Dart_NativeFunction IONativeLookup(Dart_Handle name,
   return NULL;
 }
 
+
+const char* IONativeReverseLookup(Dart_NativeFunction nf) {
+  int num_entries = sizeof(IOEntries) / sizeof(struct NativeEntries);
+  for (int i = 0; i < num_entries; i++) {
+    struct NativeEntries* entry = &(IOEntries[i]);
+    if (reinterpret_cast<Dart_NativeFunction>(entry->function_) == nf) {
+      return entry->name_;
+    }
+  }
+  return NULL;
+}
+
 }  // namespace bin
 }  // namespace dart