cps-ir: Support foreign code.

pkg/compiler/lib/src/js_backend/codegen/js_tree_builder.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.
 
 library js_tree_ir_builder;
 
 import '../../tree_ir/tree_ir_builder.dart' show Builder;
 import 'glue.dart' show Glue;
 import '../../dart2jslib.dart' show Selector, InternalErrorFunction;
 import '../../elements/elements.dart';
@@ skipping 60 matching lines @@
     return new CreateInstance(
         node.classElement,
         node.arguments.map(getVariableUse).toList(growable: false),
         node.typeInformation.map(getVariableUse).toList(growable: false));
   }
 
   Expression visitCreateInvocationMirror(cps_ir.CreateInvocationMirror node) {
     return new CreateInvocationMirror(node.selector,
         node.arguments.map(getVariableUse).toList(growable: false));
   }
+
+  Statement visitForeignCode(cps_ir.ForeignCode node) {
+    if (node.codeTemplate.isExpression) {
+      Expression foreignCode = new ForeignExpression(
+          node.codeTemplate,
+          node.type,
+          node.arguments.map(getVariableUse).toList(growable: false),
+          node.nativeBehavior,
+          node.dependency);
+      return continueWithExpression(node.continuation, foreignCode);
+    } else {
+      return new ForeignStatement(
+          node.codeTemplate,
+          node.type,
+          node.arguments.map(getVariableUse).toList(growable: false),
+          node.nativeBehavior,
+          node.dependency);

[Kevin Millikin (Google), 2015/06/16 11:23:10]

You should translate node.continuation in all cases, analogous to calls.

continueWithExpression does almost what we want, it will eventually generate
either an assignment expression statement (if the continuation parameter is
used) or just an expression statement if the continuation parameter is unused.

You might reconsider making a distinction between foreign expressions and
foreign statements --- they're all expressions and some happen to be expression
statements.

[Kevin Millikin (Google), 2015/06/16 11:23:10]

We discussed this offline:

1. We should make a distinction between foreign expressions and statements
somewhere (statements can't be translated to JS expressions).

2. Instead of not translating the continuation here, it would be better to just
not have a continuation in the IR in the first place.  The model would be the
IR's Throw (expression) and Rethrow.

[karlklose, 2015/06/18 09:38:15]

Acknowledged.

+    }
+  }
 }