cps-ir: Do not propagate assignments into try.

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 40c7cacafc8993d147ab68a4fa9e78413df9b017..1902e8f1a1b1399db65f7bce9ee817921f0092fb 100644
--- a/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
+++ b/pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart
@@ -420,11 +420,13 @@ class StatementRewriter extends Visitor<Statement, Expression> with PassMixin {
   }
 
   Statement visitTry(Try node) {
-    Set<Label> saved = safeForInlining;
-    safeForInlining = new Set<Label>();
-    node.tryBody = visitStatement(node.tryBody);
-    safeForInlining = saved;
-    node.catchBody = visitStatement(node.catchBody);
+    inEmptyEnvironment(() {
+      Set<Label> saved = safeForInlining;
+      safeForInlining = new Set<Label>();
+      node.tryBody = visitStatement(node.tryBody);
+      safeForInlining = saved;
+      node.catchBody = visitStatement(node.catchBody);
+    });
     return node;
   }