Track peak Zone memory usage and report it via HeapStatistics

src/base/accounting-allocator.h

Index: src/base/accounting-allocator.h
diff --git a/src/base/accounting-allocator.h b/src/base/accounting-allocator.h
index ce67f3790ef846a02f09b12101cfbf9fbcd29f59..ad2fc988cc89c29d37fc31aa1410a2f5ad277f86 100644
--- a/src/base/accounting-allocator.h
+++ b/src/base/accounting-allocator.h
@@ -21,9 +21,11 @@ class AccountingAllocator final {
   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);
 };