Turn on background compilation

runtime/vm/regexp_assembler_ir.cc

 // Copyright (c) 2014, 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/regexp_assembler_ir.h"
 
 #include "vm/bit_vector.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 417 matching lines @@
 
 ConstantInstr* IRRegExpMacroAssembler::WordCharacterMapConstant() const {
   const Library& lib = Library::Handle(Z, Library::CoreLibrary());
   const Class& regexp_class = Class::Handle(Z,
         lib.LookupClassAllowPrivate(Symbols::JSSyntaxRegExp()));
   const Field& word_character_field = Field::ZoneHandle(Z,
       regexp_class.LookupStaticField(Symbols::_wordCharacterMap()));
   ASSERT(!word_character_field.IsNull());
 
   if (word_character_field.IsUninitialized()) {
+    ASSERT(!Compiler::IsBackgroundCompilation());
     word_character_field.EvaluateInitializer();
   }
   ASSERT(!word_character_field.IsUninitialized());
 
   return new(Z) ConstantInstr(
         Instance::ZoneHandle(Z, word_character_field.StaticValue()));
 }
 
 
 ComparisonInstr* IRRegExpMacroAssembler::Comparison(
@@ skipping 1479 matching lines @@
       index_val,
       characters,
       specialization_cid_,
       TokenPosition::kNoSource));
 }
 
 
 #undef __
 
 }  // namespace dart