Get rid of recursive locks for job based recompilation

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 3088843309fbe31b3eed34d8d079719f2431241b..d2f85d972661c609129d8d54c307f748223ae0af 100644
--- a/src/optimizing-compiler-thread.h
+++ b/src/optimizing-compiler-thread.h
@@ -35,10 +35,10 @@ class OptimizingCompilerThread : public base::Thread {
         input_queue_shift_(0),
         osr_buffer_capacity_(FLAG_concurrent_recompilation_queue_length + 4),
         osr_buffer_cursor_(0),
-        task_count_(0),
         osr_hits_(0),
         osr_attempts_(0),
         blocked_jobs_(0),
+        ref_count_(1),
         tracing_enabled_(FLAG_trace_concurrent_recompilation),
         job_based_recompilation_(FLAG_job_based_recompilation),
         recompilation_delay_(FLAG_concurrent_recompilation_delay) {
@@ -140,18 +140,13 @@ class OptimizingCompilerThread : public base::Thread {
   base::TimeDelta time_spent_compiling_;
   base::TimeDelta time_spent_total_;
 
-  int task_count_;
-  // TODO(jochen): This is currently a RecursiveMutex since both Flush/Stop and
-  // Unblock try to get it, but the former methods both can call Unblock. Once
-  // job based recompilation is on by default, and the dedicated thread can be
-  // removed, this should be refactored to not use a RecursiveMutex.
-  base::RecursiveMutex task_count_mutex_;
-
   int osr_hits_;
   int osr_attempts_;
 
   int blocked_jobs_;
 
+  volatile base::AtomicWord ref_count_;
+
   // Copies of FLAG_trace_concurrent_recompilation,
   // FLAG_concurrent_recompilation_delay and
   // FLAG_job_based_recompilation that will be used from the background thread.