Add @JSName annotation for native fields and methods.

sdk/lib/_internal/compiler/implementation/lib/js_helper.dart

Index: sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
index f10d3d72408a924c2bf51196010434ddaa2dc7e6..7b046c9e48160576788e171478b5ff946933fceb 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
@@ -557,7 +557,7 @@ class Primitives {
       if (end <= kMaxApply) {
         subarray = array;
       } else {
-        subarray = JS('List<int>', r'array.slice(#, #)',
+        subarray = JS('=List', r'array.slice(#, #)',

[ahe, 2012/11/29 09:19:26]

How about adding a new foreign tag that clearly communicates what = means.

[sra1, 2012/12/04 01:31:31]

Do you mean another thing like 'JS'?
I don't think that scales, since the type is orthogonal to the JS text, and the
syntax is shared with @Returns and @Creates annotations on native methods.

We need to be able to tell the compiler types that are not expressible in Dart,
otherwise we can't tree-shake.  So =List needs to compose with other types, e.g.
'=List|Null' is the nullable type, 'ArrayBuffer|Document|String' is (approx)
what you get from an xhr response.

I thought about using type literals and combinators but it was verbose, ugly,
and difficult use, e.g.

  JS(const Union(const Exactly(List), Null), "...", x, x, x)

                       i, i + kMaxApply < end ? i + kMaxApply : end);
       }
       result = JS('String', '# + String.fromCharCode.apply(#, #)',
@@ -1220,6 +1220,23 @@ class Returns {
 }
 
 /**
+ * A metadata annotation placed on native methods and fields of native classes
+ * to specify the JavaScript name.
+ *
+ * This example declares a Dart field + getter + setter called `$dom_title` that
+ * corresponds to the JavaScript property `title`.
+ *
+ *     class Docmument native "*Foo" {
+ *       @JSName('title')
+ *       String $dom_title;
+ *     }
+ */
+class JSName {
+  final String name;
+  const JSName(this.name);
+}
+
+/**
  * Represents the type of Null. The compiler treats this specially.
  * TODO(lrn): Null should be defined in core. It's a class, like int.
  * It just happens to act differently in assignability tests and,