dart2js: Forbid # placeholders in JS function bodies.

pkg/compiler/lib/src/native/js.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of native;
 
+
+class HasCapturedPlaceholders extends js.BaseVisitor {
+
+  HasCapturedPlaceholders._();
+
+  static bool check(js.Node node) {
+    HasCapturedPlaceholders visitor = new HasCapturedPlaceholders._();
+    node.accept(visitor);
+    return visitor.found;
+  }
+
+  int enclosingFunctions = 0;
+  bool found = false;
+
+  @override
+  visitFun(js.Fun node) {
+    ++enclosingFunctions;
+    node.visitChildren(this);
+    --enclosingFunctions;
+  }
+
+  @override
+  visitInterpolatedNode(js.InterpolatedNode node) {
+    if (enclosingFunctions > 0) {
+      found = true;
+    }
+  }
+}
+
 class SideEffectsVisitor extends js.BaseVisitor {
   final SideEffects sideEffects;
   SideEffectsVisitor(this.sideEffects);
 
   void visit(js.Node node) {
     node.accept(this);
   }
 
   void visitLiteralExpression(js.LiteralExpression node) {
     sideEffects.setAllSideEffects();
@@ skipping 243 matching lines @@
         receiver.isPositional &&
         receiver.nameOrPosition == 0) {
       first = NativeThrowBehavior.MAY_THROW_ONLY_ON_FIRST_ARGUMENT_ACCESS;
     } else {
       first = NativeThrowBehavior.MAY;
     }
 
     return sequence(first, second);
   }
 }