Add TypeMirror.isSubtypeOf, TypeMirror.isAssignableTo, ClassMirror.isSubclassOf

sdk/lib/_internal/lib/js_mirrors.dart

Index: sdk/lib/_internal/lib/js_mirrors.dart
diff --git a/sdk/lib/_internal/lib/js_mirrors.dart b/sdk/lib/_internal/lib/js_mirrors.dart
index 2d27bab0de872fe8d310e9e7111db6016bdb915c..77939218ee883f38102f0ed9ed5f10e2fddd1b1a 100644
--- a/sdk/lib/_internal/lib/js_mirrors.dart
+++ b/sdk/lib/_internal/lib/js_mirrors.dart
@@ -1555,6 +1555,18 @@ class JsClassMirror extends JsTypeMirror with JsObjectMirror
     return createRuntimeType(_mangledName);
   }
 
+  bool isSubclassOf(ClassMirror other) {
+    if (other is! ClassMirror) throw new ArgumentError(other);
+    ClassMirror otherDeclaration = other.originalDeclaration;
+    ClassMirror c = this;
+    while (c != null) {
+      c = c.originalDeclaration;
+      if (c == otherDeclaration) return true;
+      c = c.superclass;
+    }
+    return false;
+  }
+
   // TODO(ahe): Implement this.
   Map<Symbol, MethodMirror> get instanceMembers
       => throw new UnimplementedError();
@@ -2156,6 +2168,9 @@ class JsFunctionTypeMirror extends BrokenClassMirror
   }
 
   // TODO(ahe): Implement this method.
+  bool isSubclassOf(ClassMirror other) => throw new UnimplementedError();
+
+  // TODO(ahe): Implement this method.
   MethodMirror get callMethod => throw new UnimplementedError();
 }