GC: Add tracing event for rescanning large objects on newspace evacuation

src/heap/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 3677 matching lines @@
   {
     GCTracer::Scope gc_scope(heap()->tracer(),
                              GCTracer::Scope::MC_UPDATE_POINTERS_TO_EVACUATED);
     SlotsBuffer::UpdateSlotsRecordedIn(heap_, migration_slots_buffer_);
     if (FLAG_trace_fragmentation_verbose) {
       PrintF("  migration slots buffer: %d\n",
              SlotsBuffer::SizeOfChain(migration_slots_buffer_));
     }
 
     if (compacting_ && was_marked_incrementally_) {
+      GCTracer::Scope gc_scope(heap()->tracer(),
+                               GCTracer::Scope::MC_RESCAN_LARGE_OBJECTS);
       // It's difficult to filter out slots recorded for large objects.
       LargeObjectIterator it(heap_->lo_space());
       for (HeapObject* obj = it.Next(); obj != NULL; obj = it.Next()) {
         // LargeObjectSpace is not swept yet thus we have to skip
         // dead objects explicitly.
         if (!IsMarked(obj)) continue;
 
         Page* p = Page::FromAddress(obj->address());
         if (p->IsFlagSet(Page::RESCAN_ON_EVACUATION)) {
           obj->Iterate(&updating_visitor);
@@ skipping 1041 matching lines @@
   SlotsBuffer* buffer = *buffer_address;
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 }  // namespace internal
 }  // namespace v8