Add trace event for phantom handle processing callback.

src/global-handles.cc

 // Copyright 2009 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/global-handles.h"
 
 #include "src/api.h"
 #include "src/v8.h"
 #include "src/vm-state-inl.h"
 
@@ skipping 533 matching lines @@
  public:
   // Takes ownership of the contents of pending_phantom_callbacks, leaving it in
   // the same state it would be after a call to Clear().
   PendingPhantomCallbacksSecondPassTask(
       List<PendingPhantomCallback>* pending_phantom_callbacks, Isolate* isolate)
       : CancelableTask(isolate) {
     pending_phantom_callbacks_.Swap(pending_phantom_callbacks);
   }
 
   void RunInternal() override {
+    TRACE_EVENT0("v8", "V8.GCPhantomHandleProcessingCallback");
     isolate()->heap()->CallGCPrologueCallbacks(
         GCType::kGCTypeProcessWeakCallbacks, kNoGCCallbackFlags);
     InvokeSecondPassPhantomCallbacks(&pending_phantom_callbacks_, isolate());
     isolate()->heap()->CallGCEpilogueCallbacks(
         GCType::kGCTypeProcessWeakCallbacks, kNoGCCallbackFlags);
   }
 
  private:
   List<PendingPhantomCallback> pending_phantom_callbacks_;
 
@@ skipping 937 matching lines @@
   blocks_[block][offset] = object;
   if (isolate->heap()->InNewSpace(object)) {
     new_space_indices_.Add(size_);
   }
   *index = size_++;
 }
 
 
 }  // namespace internal
 }  // namespace v8