[heap] Add tracing for the ArrayBufferTracker during scavenge.

Bug: v8:6992
Change-Id: I7b440e5fba9d86cca5b96438a31023580ad7dba2
Reviewed-on: https://chromium-review.googlesource.com/738229
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48963}

src/heap-symbols.h

@@ -350,6 +350,7 @@
   F(MINOR_MC_SWEEPING)                               \
   F(SCAVENGER_FAST_PROMOTE)                          \
   F(SCAVENGER_SCAVENGE)                              \
+  F(SCAVENGER_PROCESS_ARRAY_BUFFERS)                 \
   F(SCAVENGER_SCAVENGE_WEAK_GLOBAL_HANDLES_IDENTIFY) \
   F(SCAVENGER_SCAVENGE_WEAK_GLOBAL_HANDLES_PROCESS)  \
   F(SCAVENGER_SCAVENGE_PARALLEL)                     \

src/heap/gc-tracer.cc

@@ -461,6 +461,7 @@ void GCTracer::PrintNVP() const {
           "heap.external_weak_global_handles=%.2f "
           "fast_promote=%.2f "
           "scavenge=%.2f "
+          "scavenge.process_array_buffers=%.2f "
           "scavenge.roots=%.2f "
           "scavenge.weak=%.2f "
           "scavenge.weak_global_handles.identify=%.2f "
@@ -503,6 +504,7 @@ void GCTracer::PrintNVP() const {
           current_.scopes[Scope::HEAP_EXTERNAL_WEAK_GLOBAL_HANDLES],
           current_.scopes[Scope::SCAVENGER_FAST_PROMOTE],
           current_.scopes[Scope::SCAVENGER_SCAVENGE],
+          current_.scopes[Scope::SCAVENGER_PROCESS_ARRAY_BUFFERS],
           current_.scopes[Scope::SCAVENGER_SCAVENGE_ROOTS],
           current_.scopes[Scope::SCAVENGER_SCAVENGE_WEAK],
           current_

src/heap/heap.cc

@@ -1998,8 +1998,10 @@ void Heap::Scavenge() {
   // Set age mark.
   new_space_->set_age_mark(new_space_->top());
 
-  ArrayBufferTracker::FreeDeadInNewSpace(this);
-
+  {
+    TRACE_GC(tracer(), GCTracer::Scope::SCAVENGER_PROCESS_ARRAY_BUFFERS);
+    ArrayBufferTracker::FreeDeadInNewSpace(this);
+  }
   RememberedSet<OLD_TO_NEW>::IterateMemoryChunks(this, [](MemoryChunk* chunk) {
     if (chunk->SweepingDone()) {
       RememberedSet<OLD_TO_NEW>::FreeEmptyBuckets(chunk);