The shift-amount must not be anded with 31.

lib/compiler/implementation/lib/js_helper.dart

Index: lib/compiler/implementation/lib/js_helper.dart
diff --git a/lib/compiler/implementation/lib/js_helper.dart b/lib/compiler/implementation/lib/js_helper.dart
index d092d3b92747b7b5e2ee73fb1d6bc84ef27a57e6..9995935b32a80b604d564c98671d256450b2a224 100644
--- a/lib/compiler/implementation/lib/js_helper.dart
+++ b/lib/compiler/implementation/lib/js_helper.dart
@@ -163,6 +163,9 @@ shl(var a, var b) {
   // TODO(floitsch): inputs must be integers.
   if (checkNumbers(a, b)) {
     if (b < 0) throw new IllegalArgumentException(b);
+    // JavaScript only looks at the last 5 bits of the shift-amount. Shifting
+    // by 33 is hence equivalent to a shift by 1.
+    if (b > 31) return 0;
     return JS('num', @'(# << #) >>> 0', a, b);
   }
   return UNINTERCEPTED(a << b);
@@ -172,6 +175,9 @@ shr(var a, var b) {
   // TODO(floitsch): inputs must be integers.
   if (checkNumbers(a, b)) {
     if (b < 0) throw new IllegalArgumentException(b);
+    // JavaScript only looks at the last 5 bits of the shift-amount. Shifting
+    // by 33 is hence equivalent to a shift by 1.
+    if (b > 31) return 0;
     return JS('num', @'# >>> #', a, b);
   }
   return UNINTERCEPTED(a >> b);