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

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

Index: pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
index c802aa67d2ad2b0ce6913f0be26928659e082498..ecbe34348f236b86f90ef09caebc925d53e0bbd2 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
@@ -227,10 +227,11 @@ class IRTracer extends TracerUtil implements cps_ir.Visitor {
 
   visitBranch(cps_ir.Branch node) {
     String dummy = names.name(node);
-    String condition = visit(node.condition);
+    String condition = formatReference(node.condition);
     String trueCont = formatReference(node.trueContinuation);
     String falseCont = formatReference(node.falseContinuation);
-    printStmt(dummy, "Branch $condition ($trueCont, $falseCont)");
+    String strict = node.isStrictCheck ? "Strict" : "NonStrict";
+    printStmt(dummy, "Branch $condition ($trueCont, $falseCont) $strict");
   }
 
   visitSetMutable(cps_ir.SetMutable node) {
@@ -266,10 +267,6 @@ class IRTracer extends TracerUtil implements cps_ir.Visitor {
     return "Continuation ${names.name(node)}";
   }
 
-  visitIsTrue(cps_ir.IsTrue node) {
-    return "IsTrue(${names.name(node.value.definition)})";
-  }
-
   visitSetField(cps_ir.SetField node) {
     String object = formatReference(node.object);
     String field = node.field.name;
@@ -607,10 +604,6 @@ class BlockCollector implements cps_ir.Visitor {
     unexpectedNode(node);
   }
 
-  visitIsTrue(cps_ir.IsTrue node) {
-    unexpectedNode(node);
-  }
-
   visitInterceptor(cps_ir.Interceptor node) {
     unexpectedNode(node);
   }