dart2js cps: Bugfix in assignment propagation into branch conditions.

pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart

Index: pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
diff --git a/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart b/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
index 8c7a5af2e3cf161e2b3334bfcbc1e211f06c5348..9dd0d2aa211f5db652bd13c9719e2b50c2a1535c 100644
--- a/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
+++ b/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
@@ -584,17 +584,15 @@ class StatementRewriter extends Transformer implements Pass {
   }
 
   Statement visitIf(If node) {
-    node.condition = visitExpression(node.condition);
-
-    // Do not propagate assignments into branches.  Doing so will lead to code
-    // duplication.
-    // TODO(kmillikin): Rethink this. Propagating some assignments
-    // (e.g. variables) is benign.  If they can occur here, they should
-    // be handled well.

[asgerf, 2015/07/09 11:19:01]

This comment was just outdated. It's not really related to the change.

+    // Do not propagate assignments into branches.
     inEmptyEnvironment(() {
       node.thenStatement = visitStatement(node.thenStatement);
       node.elseStatement = visitStatement(node.elseStatement);
+    });
 
+    node.condition = visitExpression(node.condition);
+
+    inEmptyEnvironment(() {
       tryCollapseIf(node);
     });