Quick: Avoid node iteration for passes that don't need it.

Change-Id: Ic1f6796a29ba861cee37a31193e07b497b84eb3f
diff --git a/compiler/dex/pass.h b/compiler/dex/pass.h
index c377426..e349eed 100644
--- a/compiler/dex/pass.h
+++ b/compiler/dex/pass.h
@@ -85,6 +85,9 @@
     // Unused parameter.
     UNUSED(data);
 
+    // Passes that do all their work in Start() or End() should not allow useless node iteration.
+    DCHECK(false) << "Unsupported default Worker() used for " << GetName();
+
     // BasicBlock did not change.
     return false;
   }