Fix build breakage.

lib/compiler/implementation/ssa/optimize.dart

Index: lib/compiler/implementation/ssa/optimize.dart
===================================================================
--- lib/compiler/implementation/ssa/optimize.dart	(revision 13224)
+++ lib/compiler/implementation/ssa/optimize.dart	(working copy)
@@ -248,8 +248,12 @@
 
   bool isFixedSizeListConstructor(HInvokeStatic node) {
     Element element = node.inputs[0].element;
+    DartType defaultClass = compiler.listClass.defaultClass;
+    // TODO(ngeoffray): make sure that the only reason the List class is
+    // not resolved is because it's not being used.
     return element.isConstructor()
-        && element.enclosingElement == compiler.listClass.defaultClass.element
+        && defaultClass != null
+        && element.enclosingElement.declaration == defaultClass.element
         && node.inputs.length == 2
         && node.inputs[1].isInteger(types);
   }