dart2js cps: Generate fast checks for 'is String' and 'is bool'.

pkg/compiler/lib/src/js_backend/codegen/glue.dart

Index: pkg/compiler/lib/src/js_backend/codegen/glue.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/glue.dart b/pkg/compiler/lib/src/js_backend/codegen/glue.dart
index 076b554d5e01c979d6aa49c5e7fd29f130dec4e0..a68f06801740ca011c28db2f566aa54d8e444983 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/glue.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/glue.dart
@@ -252,4 +252,12 @@ class Glue {
 
   ClassElement get jsExtendableArrayClass => _backend.jsExtendableArrayClass;
   ClassElement get jsMutableArrayClass => _backend.jsMutableArrayClass;
+
+  bool isStringClass(ClassElement classElement) =>
+      classElement == _backend.jsStringClass ||
+      classElement == _compiler.stringClass;
+
+  bool isBoolClass(ClassElement classElement) =>
+      classElement == _backend.jsBoolClass ||
+      classElement == _compiler.boolClass;
 }