Support isExternal method on MethodMirror in the Dart VM. Not really intended for public consumptio…

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
diff --git a/runtime/lib/mirrors.cc b/runtime/lib/mirrors.cc
index 4b0f2914d2453ab1291f5a6b17ab9d013007a256..848f67dec269e61d3597c3e6be6f389db92db356 100644
--- a/runtime/lib/mirrors.cc
+++ b/runtime/lib/mirrors.cc
@@ -278,6 +278,7 @@ static RawInstance* CreateMethodMirror(const Function& func,
   kind_flags |= ((is_ctor && func.is_redirecting())
                  << Mirrors::kRedirectingCtor);
   kind_flags |= ((is_ctor && func.IsFactory()) << Mirrors::kFactoryCtor);
+  kind_flags |= (func.is_external() << Mirrors::kExternal);
   args.SetAt(5, Smi::Handle(Smi::New(kind_flags)));
 
   return CreateMirror(Symbols::_LocalMethodMirror(), args);
@@ -1974,7 +1975,6 @@ DEFINE_NATIVE_ENTRY(MethodMirror_source, 1) {
   return func.GetSource();
 }
 
-
 static RawInstance* CreateSourceLocation(const String& uri,
                                          intptr_t line,
                                          intptr_t column) {