Fix instruction removal for 'as' test; the bug caused us to stop optimizing after an 'as' test.

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 3406 matching lines @@
     if (as_bool.raw() == Bool::True().raw()) {
       AddReceiverCheck(call);
       // Remove the original push arguments.
       for (intptr_t i = 0; i < call->ArgumentCount(); ++i) {
         PushArgumentInstr* push = call->PushArgumentAt(i);
         push->ReplaceUsesWith(push->value()->definition());
         push->RemoveFromGraph();
       }
       // Remove call, replace it with 'left'.
       call->ReplaceUsesWith(left);
-      call->RemoveFromGraph();
+      ASSERT(current_iterator()->Current() == call);
+      current_iterator()->RemoveCurrentFromGraph();
       return;
     }
   }
   const String& dst_name = String::ZoneHandle(
       Symbols::New(Exceptions::kCastErrorDstName));
   AssertAssignableInstr* assert_as =
       new AssertAssignableInstr(call->token_pos(),
                                 new Value(left),
                                 new Value(instantiator),
                                 new Value(type_args),
@@ skipping 4845 matching lines @@
   }
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits.length(); i++) {
     CreateMaterializationAt(exits[i], alloc, alloc->cls(), *fields);
   }
 }
 
 
 }  // namespace dart