Add notice when parallel recompilation is disabled by tracing.

src/v8.cc

Index: src/v8.cc
diff --git a/src/v8.cc b/src/v8.cc
index 521d064129a32631eedeaec02c4e44eb5e2c2fa5..93f3efb2e3f64757998c23f858cba88db7ec931e 100644
--- a/src/v8.cc
+++ b/src/v8.cc
@@ -272,9 +272,10 @@ void V8::InitializeOncePerProcessImpl() {
     FLAG_max_new_space_size = (1 << (kPageSizeBits - 10)) * 2;
   }
 
-  if (FLAG_trace_hydrogen || FLAG_trace_hydrogen_stubs) {
-    // Tracing hydrogen do not work with parallel recompilation.
+  if (FLAG_parallel_recompilation &&
+      (FLAG_trace_hydrogen || FLAG_trace_hydrogen_stubs)) {
     FLAG_parallel_recompilation = false;
+    PrintF("Parallel recompilation has been disabled for tracing.\n");
   }
 
   if (FLAG_sweeper_threads <= 0) {