Add runtime and native entry tags

runtime/bin/builtin_natives.cc

Index: runtime/bin/builtin_natives.cc
diff --git a/runtime/bin/builtin_natives.cc b/runtime/bin/builtin_natives.cc
index 9201f5cb5d0504fda556f1cc8594ed64aec9f706..cec9badfe879a29e29401759a522f7d6621d0a9f 100644
--- a/runtime/bin/builtin_natives.cc
+++ b/runtime/bin/builtin_natives.cc
@@ -99,6 +99,18 @@ Dart_NativeFunction Builtin::NativeLookup(Dart_Handle name,
 }
 
 
+const char* Builtin::NativeReverseLookup(Dart_NativeFunction nf) {
+  int num_entries = sizeof(BuiltinEntries) / sizeof(struct NativeEntries);
+  for (int i = 0; i < num_entries; i++) {
+    struct NativeEntries* entry = &(BuiltinEntries[i]);
+    if (reinterpret_cast<Dart_NativeFunction>(entry->function_) == nf) {
+      return entry->name_;
+    }
+  }
+  return IONativeReverseLookup(nf);
+}
+
+
 // Implementation of native functions which are used for some
 // test/debug functionality in standalone dart mode.
 void FUNCTION_NAME(Logger_PrintString)(Dart_NativeArguments args) {