Precompilation: IsBackgroundCompiler() is now checked from various lookup routines.

runtime/vm/compiler.cc

 // Copyright (c) 2012, 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/compiler.h"
 
 #include "vm/assembler.h"
 
 #include "vm/ast_printer.h"
 #include "vm/block_scheduler.h"
@@ skipping 1979 matching lines @@
 DEFINE_RUNTIME_ENTRY(CompileFunction, 1) {
   const Function& function = Function::CheckedHandle(arguments.ArgAt(0));
   FATAL3("Precompilation missed function %s (%" Pd ", %s)\n",
          function.ToLibNamePrefixedQualifiedCString(),
          function.token_pos().value(),
          Function::KindToCString(function.kind()));
 }
 
 
 bool Compiler::IsBackgroundCompilation() {
-  UNREACHABLE();
   return false;
 }
 
 
 bool Compiler::CanOptimizeFunction(Thread* thread, const Function& function) {
   UNREACHABLE();
   return false;
 }
 
 
@@ skipping 83 matching lines @@
 }
 
 
 void BackgroundCompiler::EnsureInit(Thread* thread) {
   UNREACHABLE();
 }
 
 #endif  // DART_PRECOMPILED_RUNTIME
 
 }  // namespace dart