cps: Use BuiltinOperator.IsNumber for 'is num'

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

Index: pkg/compiler/lib/src/js_backend/codegen/codegen.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
index 7dced8a008409eaf6b2ed38629ec87217c35e5ff..d1d7bbad7c863d6356f87dc16d3bffe3bc75914d 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/codegen.dart
@@ -867,13 +867,13 @@ class CodeGenerator extends tree_ir.StatementVisitor
       case BuiltinOperator.IsFalsy:
         return new js.Prefix('!', args[0]);
       case BuiltinOperator.IsNumber:
-        return js.js("typeof # === 'number'", args);
+        return js.js('typeof # === "number"', args);
       case BuiltinOperator.IsNotNumber:
-        return js.js("typeof # !== 'number'", args);
+        return js.js('typeof # !== "number"', args);
       case BuiltinOperator.IsFloor:
-        return js.js("Math.floor(#) === #", args);
+        return js.js('Math.floor(#) === #', args);
       case BuiltinOperator.IsNumberAndFloor:
-        return js.js("typeof # === 'number' && Math.floor(#) === #", args);
+        return js.js('typeof # === "number" && Math.floor(#) === #', args);
     }
   }