Implement metadata as an internal native. Be honest about which mirrors don't yet support metadata …

runtime/lib/mirrors.cc

Index: runtime/lib/mirrors.cc
===================================================================
--- runtime/lib/mirrors.cc	(revision 25060)
+++ runtime/lib/mirrors.cc	(working copy)
@@ -631,7 +631,7 @@
 
 static Dart_Handle CreateVariableMirror(Dart_Handle var,
                                         Dart_Handle var_name,
-                                        Dart_Handle lib_mirror) {
+                                        Dart_Handle owner_mirror) {
   ASSERT(Dart_IsVariable(var));
   Dart_Handle cls_name = NewString("_LocalVariableMirrorImpl");
   Dart_Handle type = Dart_GetType(MirrorLib(), cls_name, 0, NULL);
@@ -657,8 +657,9 @@
   }
 
   Dart_Handle args[] = {
+    CreateMirrorReference(var),
     var_name,
-    lib_mirror,
+    owner_mirror,
     CreateLazyMirror(var_type),
     Dart_NewBoolean(is_static),
     Dart_NewBoolean(is_final),
@@ -1112,18 +1113,25 @@
   Dart_ExitScope();
 }
 
-void NATIVE_ENTRY_FUNCTION(Mirrors_metadata)(Dart_NativeArguments args) {
-  Dart_EnterScope();
-  Dart_Handle mirror = Dart_GetNativeArgument(args, 0);
 
-  Dart_Handle reflectee = UnwrapMirror(mirror);
-  Dart_Handle result = Dart_GetMetadata(reflectee);
-  if (Dart_IsError(result)) {
-    Dart_PropagateError(result);
+DEFINE_NATIVE_ENTRY(DeclarationMirror_metadata, 1) {
+  const MirrorReference& decl_ref =
+      MirrorReference::CheckedHandle(arguments->NativeArgAt(0));
+  const Object& decl = Object::Handle(decl_ref.referent());
+
+  Class& klass = Class::Handle();
+  if (decl.IsClass()) {
+    klass ^= decl.raw();
+  } else if (decl.IsFunction()) {
+    klass = Function::Cast(decl).origin();
+  } else if (decl.IsField()) {
+    klass = Field::Cast(decl).origin();
+  } else {
+    return Object::empty_array().raw();
   }
-  ASSERT(Dart_IsList(result));
-  Dart_SetReturnValue(args, result);
-  Dart_ExitScope();
+
+  const Library& library = Library::Handle(klass.library());
+  return library.GetMetadata(decl);
 }