Don't always slow-path array casts/instance-of.

Recent changes to IsAbstract for arrays pushed us in to always generating
slow-paths.

Change-Id: I52fb50953949f337243961a308eabf0d684eacf3
diff --git a/src/compiler/driver/compiler_driver.cc b/src/compiler/driver/compiler_driver.cc
index 186cf0d..b04e5b1 100644
--- a/src/compiler/driver/compiler_driver.cc
+++ b/src/compiler/driver/compiler_driver.cc
@@ -851,7 +851,7 @@
       *type_known_final = resolved_class->IsFinal() && !resolved_class->IsArrayClass();
     }
     if (type_known_abstract != NULL) {
-      *type_known_abstract = resolved_class->IsAbstract();
+      *type_known_abstract = resolved_class->IsAbstract() && !resolved_class->IsArrayClass();
     }
   } else {
     stats_->TypeNeedsAccessCheck();