dart2js cps: Add instruction for bounds checks.

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 6c7469ee96ce2a25cbc2a9316332ec1402191106..e19b23e4f15a3dc9b9147f0ad73fde92c29dd678 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_tracer.dart
@@ -389,6 +389,17 @@ class IRTracer extends TracerUtil implements cps_ir.Visitor {
     String value = formatReference(node.value);
     return 'Refinement $value ${node.refineType}';
   }
+
+  visitBoundsCheck(cps_ir.BoundsCheck node) {
+    String object = formatReference(node.object);
+    String index = node.index == null
+        ? 'no-index'
+        : formatReference(node.index);
+    String length = node.length == null
+        ? 'no-length'
+        : formatReference(node.length);
+    return 'BoundsCheck $object $index $length ${node.checkString}';
+  }
 }
 
 /**
@@ -671,4 +682,8 @@ class BlockCollector implements cps_ir.Visitor {
   visitRefinement(cps_ir.Refinement node) {
     unexpectedNode(node);
   }
+
+  visitBoundsCheck(cps_ir.BoundsCheck node) {
+    unexpectedNode(node);
+  }
 }