Silence control reducer tracing a bit.

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 6951d8c8b5dcc51201829d0f5a25a502e3a77c22..5a21b183bc097bcce8acb62c5ac3e5376370c6d7 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -353,8 +353,9 @@ DEFINE_STRING(turbo_filter, "~", "optimization filter for TurboFan compiler")
 DEFINE_BOOL(trace_turbo, false, "trace generated TurboFan IR")
 DEFINE_STRING(trace_turbo_cfg_file, NULL,
               "trace turbo cfg graph (for C1 visualizer) to a given file name")
-DEFINE_BOOL(trace_turbo_types, true, "trace generated TurboFan types")
-DEFINE_BOOL(trace_turbo_scheduler, false, "trace generated TurboFan scheduler")
+DEFINE_BOOL(trace_turbo_types, true, "trace TurboFan's types")
+DEFINE_BOOL(trace_turbo_scheduler, false, "trace TurboFan's scheduler")
+DEFINE_BOOL(trace_turbo_reduction, false, "trace TurboFan's various reducers")
 DEFINE_BOOL(turbo_asm, false, "enable TurboFan for asm.js code")
 DEFINE_BOOL(turbo_verify, false, "verify TurboFan graphs at each phase")
 DEFINE_BOOL(turbo_stats, false, "print TurboFan statistics")