[heap] Print marking worklist only in debug mode.

This save ~40KB of code size in release mode.

Bug: 
Change-Id: Ibdf7e64bb2592f53a4edf07665016dd5a65714a0
Reviewed-on: https://chromium-review.googlesource.com/801515Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49769}

src/heap/incremental-marking.cc

@@ -990,10 +990,14 @@ size_t IncrementalMarking::Step(size_t bytes_to_process,
       marking_worklist()->shared()->MergeGlobalPool(
           marking_worklist()->on_hold());
     }
+
+// Only print marking worklist in debug mode to save ~40KB of code size.
+#ifdef DEBUG
     if (FLAG_trace_incremental_marking && FLAG_trace_concurrent_marking &&
         FLAG_trace_gc_verbose) {
       marking_worklist()->Print();
     }
+#endif
 
     if (worklist_to_process == WorklistToProcess::kBailout) {
       bytes_processed =