Support for extending native classes

sdk/lib/_internal/lib/interceptors.dart

Index: sdk/lib/_internal/lib/interceptors.dart
diff --git a/sdk/lib/_internal/lib/interceptors.dart b/sdk/lib/_internal/lib/interceptors.dart
index 5e6e77e46a59fdb76722bf1640ad2e152c31b520..464b2db70110492beafc4b6cb139d966204858ed 100644
--- a/sdk/lib/_internal/lib/interceptors.dart
+++ b/sdk/lib/_internal/lib/interceptors.dart
@@ -25,7 +25,7 @@ import 'dart:_js_helper' show allMatchesInStringUnchecked,
                               lookupDispatchRecord,
                               StringMatch,
                               firstMatchAfter;
-import 'dart:_foreign_helper' show JS;
+import 'dart:_foreign_helper' show JS, JS_EFFECT;
 
 part 'js_array.dart';
 part 'js_number.dart';
@@ -246,6 +246,37 @@ void initializeDispatchPropertyCSP(
  */
 var interceptedNames;
 
+
+/**
+ * Data structure used to map a [Type] to the [Interceptor] for that type.  It
+ * is JavaScript array of 2N entries of adjacent slots containing a [Type]
+ * followed by an [Interceptor] class for the type.

[ahe, 2013/08/13 18:31:47]

I'm not sure how critical this is for performance, but I think you could easily
use a JS object literal. '$type' is a mangled name that is safe to use as a key
in a JS object.

Note: I'm planning on changing that for mirrors, but I will provide a method to
extract the mangled name from a Type object.

Also note: I'm about to add a class that makes it rather convenient to work with
caches based on JS object literals. Look for JsCache in js_helper.dart.

[sra1, 2013/08/14 04:36:47]

It is not critical, at least for now.  For the type to be added to this list,
the type must already be in the constant pool.
Unless you can do that for free, it will require metadata which might not
otherwise be required.  This list is the intersection of constant-pool types and
subtypes of native types which would usually be much smaller

+ *
+ * The value of this variable is set by the compiler and contains only types
+ * that are user extensions of native classes where the type occurs as a
+ * constant in the program.
+ */
+// TODO(sra): Mark this as initialized to a constant with unknown value.
+var mapTypeToInterceptor;
+
+findClassConstructorForType(Type type) {
+  JS_EFFECT((_){ mapTypeToInterceptor = _; });
+  if (mapTypeToInterceptor == null) return null;
+  List map = JS('JSFixedArray', '#', mapTypeToInterceptor);
+  for (int i = 0; i + 1 < map.length; i += 2) {
+    if (type == map[i]) {
+      return map[i + 1];
+    }
+  }
+  return null;
+}
+
+findInterceptorForType(Type type) {
+  var constructor = findClassConstructorForType(type);
+  if (constructor == null) return null;
+  return JS('', '#.prototype', constructor);
+}
+
 /**
  * The base interceptor class.
  *