Minor work for background compilation

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 1508 matching lines @@
     const Object& result = PassiveObject::Handle(thread->sticky_error());
     thread->clear_sticky_error();
     return result.raw();
   }
   UNREACHABLE();
   return Object::null();
 }
 
 
 void Compiler::AbortBackgroundCompilation(intptr_t deopt_id) {
+  if (FLAG_trace_compiler) {
+    THR_Print("ABORT background compilation.");
+  }
   ASSERT(Compiler::IsBackgroundCompilation());
   Thread::Current()->long_jump_base()->Jump(
       deopt_id, Object::background_compilation_error());
 }
 
 
 // C-heap allocated background compilation queue element.
 class QueueElement {
  public:
   explicit QueueElement(const Function& function)
@@ skipping 345 matching lines @@
 }
 
 
 void BackgroundCompiler::EnsureInit(Thread* thread) {
   UNREACHABLE();
 }
 
 #endif  // DART_PRECOMPILED_RUNTIME
 
 }  // namespace dart