Extension method support to move us closer to a valid List implementation.

tool/input_sdk/lib/core/annotations.dart

Index: tool/input_sdk/lib/core/annotations.dart
diff --git a/tool/input_sdk/lib/core/annotations.dart b/tool/input_sdk/lib/core/annotations.dart
index 5ceed34fd63bb8b0f3123bb06c892afa9cbe3d5e..8433b8baac53f6f8f38925a4e640f99196131c5e 100644
--- a/tool/input_sdk/lib/core/annotations.dart
+++ b/tool/input_sdk/lib/core/annotations.dart
@@ -4,6 +4,31 @@
 
 part of dart.core;
 
+// TODO(jacobr): move these annotations to a different package. E.g. dart:js
+
+class JsName {
+  /// The JavaScript name.
+  /// Used for classes and libraries.
+  /// Note that this could be an expression, e.g. `lib.TypeName` in JS, but it
+  /// should be kept simple, as it will be generated directly into the code.
+  final String name;
+  const JsName({this.name});
+}
+
+class JsPeerInterface {
+  /// The JavaScript type that we should match the API of.
+  /// Used for classes where Dart subclasses should be callable from JavaScript
+  /// matching the JavaScript calling conventions.
+  final String name;
+  const JsPeerInterface({this.name});
+}
+
+/// Whether an interface is allowed to have JavaScript implementations that

[vsm, 2015/04/03 16:41:20]

Perhaps: A Dart interface may only be implemented by a native JavaScript object
if it is marked with this annotation.

Is that correct?

[Jacob, 2015/04/03 20:25:59]

That is correct and clearer. Done.

+/// use extension methods to provide custom Dart behavior.
+class SupportJsExtensionMethod {

[Jennifer Messerly, 2015/04/03 16:25:29]

supports?

[Jacob, 2015/04/03 20:25:59]

This annotation name is bad. Got any better ideas?
Maybe 
@JsExtensionMethodImplementation
or
@NativeJsImplementation
?

+  const SupportJsExtensionMethod();
+}
+
 /**
  * The annotation `@Deprecated('expires when')` marks a feature as deprecated.
  *