[heap] Bound number of tasks by embedder limit instead of artificially capping

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 102 matching lines @@
       while (item != nullptr) {
         bool success = (item->state.Value() == kFinished);
         JobTraits::FinalizePageSequentially(heap_, item->chunk, success,
                                             item->data);
         item = item->next;
       }
     }
   }
 
  private:
-  static const int kMaxNumberOfTasks = 10;
+  static const int kMaxNumberOfTasks = 32;
 
   enum ProcessingState { kAvailable, kProcessing, kFinished, kFailed };
 
   struct Item : public Malloced {
     Item(MemoryChunk* chunk, typename JobTraits::PerPageData data, Item* next)
         : chunk(chunk), state(kAvailable), data(data), next(next) {}
     MemoryChunk* chunk;
     base::AtomicValue<ProcessingState> state;
     typename JobTraits::PerPageData data;
     Item* next;
@@ skipping 52 matching lines @@
   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_