cps-ir: Support foreign code.

pkg/compiler/lib/src/js_backend/codegen/js_tree_builder.dart

Index: pkg/compiler/lib/src/js_backend/codegen/js_tree_builder.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/js_tree_builder.dart b/pkg/compiler/lib/src/js_backend/codegen/js_tree_builder.dart
index 98893f8630bc428eeee63f59cefd720693a1d612..1e2c5025382e6900840689ecf69367b73812622e 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/js_tree_builder.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/js_tree_builder.dart
@@ -78,4 +78,23 @@ class JsTreeBuilder extends Builder {
     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.

+    }
+  }
 }