Add mutex when accessing concurrent recompilation output queue.

src/optimizing-compiler-thread.h

Index: src/optimizing-compiler-thread.h
diff --git a/src/optimizing-compiler-thread.h b/src/optimizing-compiler-thread.h
index d1ed6a2c59fada05467a2f1a4182710a9bef7976..42317657024fbc3ced25ec8381d231225728e29c 100644
--- a/src/optimizing-compiler-thread.h
+++ b/src/optimizing-compiler-thread.h
@@ -115,7 +115,7 @@ class OptimizingCompilerThread : public Thread {
   UnboundQueue<OptimizingCompiler*> input_queue_;
   // Queue of recompilation tasks ready to be installed (excluding OSR).
   UnboundQueue<OptimizingCompiler*> output_queue_;
-  // List of all OSR related recompilation tasks (both incoming and ready ones).
+  // List of recompilation tasks for OSR in the input queue.
   List<OptimizingCompiler*> osr_candidates_;
   // List of recompilation tasks ready for OSR.
   List<OptimizingCompiler*> ready_for_osr_;
@@ -125,6 +125,8 @@ class OptimizingCompilerThread : public Thread {
   TimeDelta time_spent_compiling_;
   TimeDelta time_spent_total_;
 
+  // TODO(yangguo): remove this once the memory leak has been figured out.
+  Mutex queue_mutex_;
   Mutex osr_list_mutex_;
   int osr_hits_;
   int osr_attempts_;