dart2js cps: Use a strictness flag on Branch instead of rewriting.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
index a04fb4eb5d170003055ba4d5d5961cfb0a0ed469..988ee694ade8b9fc08beb11167b7ad0b2d7c9368 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.dart
@@ -192,10 +192,11 @@ class SExpressionStringifier extends Indentation implements Visitor<String> {
   }
 
   String visitBranch(Branch node) {
-    String condition = visit(node.condition);
+    String condition = access(node.condition);
     String trueCont = access(node.trueContinuation);
     String falseCont = access(node.falseContinuation);
-    return '$indentation(Branch $condition $trueCont $falseCont)';
+    String strict = node.isStrictCheck ? 'Strict' : 'NonStrict';
+    return '$indentation(Branch $condition $trueCont $falseCont $strict)';
   }
 
   String visitUnreachable(Unreachable node) {
@@ -251,11 +252,6 @@ class SExpressionStringifier extends Indentation implements Visitor<String> {
     return '(LiteralMap ($keys) ($values))';
   }
 
-  String visitIsTrue(IsTrue node) {
-    String value = access(node.value);
-    return '(IsTrue $value)';
-  }
-
   String visitSetField(SetField node) {
     String object = access(node.object);
     String field = node.field.name;