Update from chromium https://crrev.com/301315

base/memory/discardable_memory_mach.h

 // Copyright 2014 The Chromium 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 BASE_MEMORY_DISCARDABLE_MEMORY_MACH_H_
 #define BASE_MEMORY_DISCARDABLE_MEMORY_MACH_H_
 
 #include "base/memory/discardable_memory.h"
 
 #include "base/mac/scoped_mach_vm.h"
@@ skipping 15 matching lines @@
 
   // Overridden from DiscardableMemory:
   DiscardableMemoryLockStatus Lock() override;
   void Unlock() override;
   void* Memory() const override;
 
   // Overridden from internal::DiscardableMemoryManagerAllocation:
   bool AllocateAndAcquireLock() override;
   void ReleaseLock() override;
   void Purge() override;
+  bool IsMemoryResident() const override;
 
  private:
   mac::ScopedMachVM memory_;
   const size_t bytes_;
   bool is_locked_;
 
   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryMach);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_MACH_H_