Instrument callers of Semaphore::Signal to help with investigation of

src/heap/page-parallel-job.h

 // Copyright 2016 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.
 
 #ifndef V8_HEAP_PAGE_PARALLEL_JOB_
 #define V8_HEAP_PAGE_PARALLEL_JOB_
 
 #include "src/allocation.h"
 #include "src/cancelable-task.h"
 #include "src/utils.h"
@@ skipping 143 matching lines @@
           bool success = JobTraits::ProcessPageInParallel(
               heap_, data_, current->chunk, current->data);
           current->state.SetValue(success ? kFinished : kFailed);
         }
         current = current->next;
         // Wrap around if needed.
         if (current == nullptr) {
           current = items_;
         }
       }
-      on_finish_->Signal();
+      on_finish_->Signal("PageParallelJob::Task::RunInternal");
     }
 
     Heap* heap_;
     Item* items_;
     int num_items_;
     int start_index_;
     base::Semaphore* on_finish_;
     typename JobTraits::PerTaskData data_;
     DISALLOW_COPY_AND_ASSIGN(Task);
   };
 
   Heap* heap_;
   CancelableTaskManager* cancelable_task_manager_;
   Item* items_;
   int num_items_;
   int num_tasks_;
   base::Semaphore* pending_tasks_;
   DISALLOW_COPY_AND_ASSIGN(PageParallelJob);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_PAGE_PARALLEL_JOB_