Eliminate dependencies on assemblers and code stubs in precompiled runtime.

runtime/vm/branch_optimizer.cc

Index: runtime/vm/branch_optimizer.cc
diff --git a/runtime/vm/branch_optimizer.cc b/runtime/vm/branch_optimizer.cc
index 0048b7ed637da3a17cc9cff4b85cb046595f6954..ab14964a86a3ad9d86c5a35c9dc58402a5346189 100644
--- a/runtime/vm/branch_optimizer.cc
+++ b/runtime/vm/branch_optimizer.cc
@@ -2,6 +2,8 @@
 // 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.
 
+#if !defined(DART_PRECOMPILED_RUNTIME)
+
 #include "vm/branch_optimizer.h"
 
 #include "vm/flow_graph.h"
@@ -348,3 +350,5 @@ void IfConverter::Simplify(FlowGraph* flow_graph) {
 
 
 }  // namespace dart
+
+#endif  // !defined(DART_PRECOMPILED_RUNTIME)