Update from https://crrev.com/320343

base/memory/discardable_memory_manager.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_MANAGER_H_
-#define BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_
-
-#include "base/base_export.h"
-#include "base/containers/hash_tables.h"
-#include "base/containers/mru_cache.h"
-#include "base/synchronization/lock.h"
-#include "base/time/time.h"
-
-namespace base {
-namespace internal {
-
-// This interface is used by the DiscardableMemoryManager class to provide some
-// level of userspace control over discardable memory allocations.
-class DiscardableMemoryManagerAllocation {
- public:
-  // Allocate and acquire a lock that prevents the allocation from being purged
-  // by the system. Returns true if memory was previously allocated and is still
-  // resident.
-  virtual bool AllocateAndAcquireLock() = 0;
-
-  // Release a previously acquired lock on the allocation so that it can be
-  // purged by the system.
-  virtual void ReleaseLock() = 0;
-
-  // Explicitly purge this allocation. It is illegal to call this while a lock
-  // is acquired on the allocation.
-  virtual void Purge() = 0;
-
- protected:
-  virtual ~DiscardableMemoryManagerAllocation() {}
-};
-
-}  // namespace internal
-}  // namespace base
-
-namespace base {
-namespace internal {
-
-// The DiscardableMemoryManager manages a collection of
-// DiscardableMemoryManagerAllocation instances. It is used on platforms that
-// need some level of userspace control over discardable memory. It keeps track
-// of all allocation instances (in case they need to be purged), and the total
-// amount of allocated memory (in case this forces a purge). When memory usage
-// reaches the limit, the manager purges the LRU memory.
-class BASE_EXPORT_PRIVATE DiscardableMemoryManager {
- public:
-  typedef DiscardableMemoryManagerAllocation Allocation;
-
-  DiscardableMemoryManager(size_t memory_limit,
-                           size_t soft_memory_limit,
-                           TimeDelta hard_memory_limit_expiration_time);
-  virtual ~DiscardableMemoryManager();
-
-  // The maximum number of bytes of memory that may be allocated before we force
-  // a purge.
-  void SetMemoryLimit(size_t bytes);
-
-  // The number of bytes of memory that may be allocated but unused for the hard
-  // limit expiration time without getting purged.
-  void SetSoftMemoryLimit(size_t bytes);
-
-  // Sets the memory usage cutoff time for hard memory limit.
-  void SetHardMemoryLimitExpirationTime(
-      TimeDelta hard_memory_limit_expiration_time);
-
-  // This will attempt to reduce memory footprint until within soft memory
-  // limit. Returns true if there's no need to call this again until allocations
-  // have been used.
-  bool ReduceMemoryUsage();
-
-  // This can be called to attempt to reduce memory footprint until within
-  // limit for bytes to keep under moderate pressure.
-  void ReduceMemoryUsageUntilWithinLimit(size_t bytes);
-
-  // Adds the given allocation to the manager's collection.
-  void Register(Allocation* allocation, size_t bytes);
-
-  // Removes the given allocation from the manager's collection.
-  void Unregister(Allocation* allocation);
-
-  // Returns false if an error occurred. Otherwise, returns true and sets
-  // |purged| to indicate whether or not allocation has been purged since last
-  // use.
-  bool AcquireLock(Allocation* allocation, bool* purged);
-
-  // Release a previously acquired lock on allocation. This allows the manager
-  // to purge it if necessary.
-  void ReleaseLock(Allocation* allocation);
-
-  // Purges all discardable memory.
-  void PurgeAll();
-
-  // Returns true if allocation has been added to the manager's collection. This
-  // should only be used by tests.
-  bool IsRegisteredForTest(Allocation* allocation) const;
-
-  // Returns true if allocation can be purged. This should only be used by
-  // tests.
-  bool CanBePurgedForTest(Allocation* allocation) const;
-
-  // Returns total amount of allocated discardable memory. This should only be
-  // used by tests.
-  size_t GetBytesAllocatedForTest() const;
-
- private:
-  struct AllocationInfo {
-    explicit AllocationInfo(size_t bytes) : bytes(bytes), purgable(false) {}
-
-    const size_t bytes;
-    bool purgable;
-    TimeTicks last_usage;
-  };
-  typedef HashingMRUCache<Allocation*, AllocationInfo> AllocationMap;
-
-  // Purges memory not used since |hard_memory_limit_expiration_time_| before
-  // "right now" until usage is less or equal to |soft_memory_limit_|.
-  // Returns true if total amount of memory is less or equal to soft memory
-  // limit.
-  bool PurgeIfNotUsedSinceHardLimitCutoffUntilWithinSoftMemoryLimit();
-
-  // Purges memory that has not been used since |timestamp| until usage is less
-  // or equal to |limit|.
-  // Caller must acquire |lock_| prior to calling this function.
-  void PurgeIfNotUsedSinceTimestampUntilUsageIsWithinLimitWithLockAcquired(
-      TimeTicks timestamp,
-      size_t limit);
-
-  // Called when a change to |bytes_allocated_| has been made.
-  void BytesAllocatedChanged(size_t new_bytes_allocated) const;
-
-  // Virtual for tests.
-  virtual TimeTicks Now() const;
-
-  // Needs to be held when accessing members.
-  mutable Lock lock_;
-
-  // A MRU cache of all allocated bits of memory. Used for purging.
-  AllocationMap allocations_;
-
-  // The total amount of allocated memory.
-  size_t bytes_allocated_;
-
-  // The maximum number of bytes of memory that may be allocated.
-  size_t memory_limit_;
-
-  // The number of bytes of memory that may be allocated but not used for
-  // |hard_memory_limit_expiration_time_| amount of time when receiving an idle
-  // notification.
-  size_t soft_memory_limit_;
-
-  // Amount of time it takes for an allocation to become affected by
-  // |soft_memory_limit_|.
-  TimeDelta hard_memory_limit_expiration_time_;
-
-  DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryManager);
-};
-
-}  // namespace internal
-}  // namespace base
-
-#endif  // BASE_MEMORY_DISCARDABLE_MEMORY_MANAGER_H_