Rename "parallel recompilation" to "concurrent 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 cbd4d0e48724a3577a51fda93d0675567b77df38..aff94eddc22429b0aeadd05f830e515d7e544eb4 100644
--- a/src/optimizing-compiler-thread.h
+++ b/src/optimizing-compiler-thread.h
@@ -75,7 +75,7 @@ class OptimizingCompilerThread : public Thread {
     // only one thread can run inside an Isolate at one time, a direct
     // doesn't introduce a race -- queue_length_ may decreased in
     // meantime, but not increased.
-    return (current_length < FLAG_parallel_recompilation_queue_length);
+    return (current_length < FLAG_concurrent_recompilation_queue_length);
   }
 
 #ifdef DEBUG