[heap] Report reduce memory GCs in --trace-gc

Let --trace-gc now also emit whether the GC is a memory reducing GC or not.

Change-Id: If0efd9e9a52d9cb861ca9692a2c93812effeabaa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2064220Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66389}

src/heap/gc-tracer.cc

@@ -518,11 +518,12 @@ void GCTracer::Print() const {
   Output(
       "[%d:%p] "
       "%8.0f ms: "
-      "%s %.1f (%.1f) -> %.1f (%.1f) MB, "
+      "%s%s %.1f (%.1f) -> %.1f (%.1f) MB, "
       "%.1f / %.1f ms %s (average mu = %.3f, current mu = %.3f) %s %s\n",
       base::OS::GetCurrentProcessId(),
       reinterpret_cast<void*>(heap_->isolate()),
       heap_->isolate()->time_millis_since_init(), current_.TypeName(false),
+      current_.reduce_memory ? " (reduce)" : "",
       static_cast<double>(current_.start_object_size) / MB,
       static_cast<double>(current_.start_memory_size) / MB,
       static_cast<double>(current_.end_object_size) / MB,