Better constant fold identity checks. (100 bytes saved on swarm, yeah! :))

lib/compiler/implementation/ssa/nodes.dart

Index: lib/compiler/implementation/ssa/nodes.dart
===================================================================
--- lib/compiler/implementation/ssa/nodes.dart	(revision 6994)
+++ lib/compiler/implementation/ssa/nodes.dart	(working copy)
@@ -874,6 +874,7 @@
   }
 
   bool isConstant() => false;
+  bool isConstantBoolean() => false;
   bool isConstantNull() => false;
   bool isConstantNumber() => false;
   bool isConstantString() => false;
@@ -1868,10 +1869,10 @@
   accept(HVisitor visitor) => visitor.visitEquals(this);
 
   bool get builtin() {
-    // All useful types have === semantics.
+    // All primitive types have === semantics.
     // Note that this includes all constants except the user-constructed
     // objects.
-    return left.isConstantNull() || left.propagatedType.isUseful();
+    return left.isConstantNull() || left.propagatedType.isPrimitive();
   }
 
   HType computeTypeFromInputTypes() {