Track peak Zone memory usage and report it via HeapStatistics

src/base/accounting-allocator.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_BASE_ACCOUNTING_ALLOCATOR_H_
 #define V8_BASE_ACCOUNTING_ALLOCATOR_H_
 
 #include "src/base/atomicops.h"
 #include "src/base/macros.h"
 
 namespace v8 {
 namespace base {
 
 class AccountingAllocator final {
  public:
   AccountingAllocator() = default;
   ~AccountingAllocator() = default;
 
   // Returns nullptr on failed allocation.
   void* Allocate(size_t bytes);
   void Free(void* memory, size_t bytes);
 
   size_t GetCurrentMemoryUsage() const;
+  size_t GetMaxMemoryUsage() const;
 
  private:
   AtomicWord current_memory_usage_ = 0;
+  AtomicWord max_memory_usage_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(AccountingAllocator);
 };
 
 }  // namespace base
 }  // namespace v8
 
 #endif  // V8_BASE_ACCOUNTING_ALLOCATOR_H_