dart2js cps: Handle native functions, getters, and setters.

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
index 79731e783359e9743f581d5bdabe3286c9cfa4c6..2f90ddf8f9358c3c006bdf82d36e69a981ccf0d5 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
@@ -405,13 +405,16 @@ abstract class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
   //   where (C', x) = Build(e, C)
   //
   // Return without a subexpression is translated as if it were return null.
-  ir.Primitive visitReturn(ast.Return node) {
+  visitReturn(ast.Return node) {
     assert(irBuilder.isOpen);
-    assert(invariant(node, node.beginToken.value != 'native'));
-    irBuilder.buildReturn(
-        value: build(node.expression),
-        sourceInformation: sourceInformationBuilder.buildReturn(node));
-    return null;
+    SourceInformation source = sourceInformationBuilder.buildReturn(node);
+    if (node.beginToken.value == 'native') {
+      irBuilder.buildNativeFunctionBody(node.expression, source);
+    } else {
+      irBuilder.buildReturn(
+          value: build(node.expression),
+          sourceInformation: source);
+    }
   }
 
   visitSwitchStatement(ast.SwitchStatement node) {
@@ -2281,12 +2284,23 @@ class GlobalProgramInformation {
   DartType unaliasType(DartType type) => type.unalias(_compiler);
 
   TypeMask getTypeMaskForForeign(NativeBehavior behavior) {
+    if (behavior == null) {
+      return _backend.dynamicType;
+    }
     return TypeMaskFactory.fromNativeBehavior(behavior, _compiler);
   }
 
   FieldElement locateSingleField(Selector selector, TypeMask type) {
     return _compiler.world.locateSingleField(selector, type);
   }
+
+  Element get closureConverter {
+    return _backend.getClosureConverter();
+  }
+
+  void addNativeMethod(FunctionElement function) {
+    _backend.emitter.nativeEmitter.nativeMethods.add(function);
+  }
 }
 
 /// IR builder specific to the JavaScript backend, coupled to the [JsIrBuilder].