Add ClassMirror.isAbstract to the API and VM implementation.

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 18829bf7038177cfd16067e19184be43f43138a3..2d27bab0de872fe8d310e9e7111db6016bdb915c 100644
--- a/sdk/lib/_internal/lib/js_mirrors.dart
+++ b/sdk/lib/_internal/lib/js_mirrors.dart
@@ -774,6 +774,8 @@ class JsMixinApplication extends JsTypeMirror with JsObjectMirror
 
   // TODO(ahe): Implement this.
   Function operator [](Symbol name) => throw new UnimplementedError();
+
+  bool get isAbstract => throw new UnimplementedError();
 }
 
 abstract class JsObjectMirror implements ObjectMirror {
@@ -1146,6 +1148,8 @@ class JsTypeBoundClassMirror extends JsDeclarationMirror
 
   bool get isTopLevel => _class.isTopLevel;
 
+  bool get isAbstract => _class.isAbstract;
+
   SourceLocation get location => _class.location;
 
   MirrorSystem get mirrors => _class.mirrors;
@@ -1563,6 +1567,8 @@ class JsClassMirror extends JsTypeMirror with JsObjectMirror
 
   // TODO(ahe): Implement this.
   Function operator [](Symbol name) => throw new UnimplementedError();
+
+  bool get isAbstract => throw new UnimplementedError();
 }
 
 class JsVariableMirror extends JsDeclarationMirror implements VariableMirror {
@@ -2070,6 +2076,8 @@ class JsFunctionTypeMirror extends BrokenClassMirror
   get _namedArguments => JS('=Object', '#.named', _typeData);
   bool get isOriginalDeclaration => true;
 
+  bool get isAbstract => false;
+
   TypeMirror get returnType {
     if (_cachedReturnType != null) return _cachedReturnType;
     if (_isVoid) return _cachedReturnType = JsMirrorSystem._voidType;