Re-land: base: Implement browser process support for discardable memory.

content/common/host_discardable_shared_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 CONTENT_COMMON_HOST_DISCARDABLE_SHARED_MEMORY_MANAGER_H_
 #define CONTENT_COMMON_HOST_DISCARDABLE_SHARED_MEMORY_MANAGER_H_
 
 #include <vector>
 
 #include "base/memory/discardable_memory_shmem_allocator.h"
@@ skipping 53 matching lines @@
     linked_ptr<base::DiscardableSharedMemory> memory;
     base::ProcessHandle process_handle;
   };
 
   static bool CompareMemoryUsageTime(const MemorySegment& a,
                                      const MemorySegment& b) {
     // In this system, LRU memory segment is evicted first.
     return a.memory->last_known_usage() > b.memory->last_known_usage();
   }
 
+  void AllocateLockedDiscardableSharedMemory(
+      base::ProcessHandle process_handle,
+      size_t size,
+      base::SharedMemoryHandle* shared_memory_handle);
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
   void ReduceMemoryUsageUntilWithinMemoryLimit();
   void ReduceMemoryUsageUntilWithinLimit(size_t limit);
   void BytesAllocatedChanged(size_t new_bytes_allocated) const;
 
   // Virtual for tests.
   virtual base::Time Now() const;
   virtual void ScheduleEnforceMemoryPolicy();
 
   base::Lock lock_;
   // Note: The elements in |segments_| are arranged in such a way that they form
   // a heap. The LRU memory segment always first.
   typedef std::vector<MemorySegment> MemorySegmentVector;
   MemorySegmentVector segments_;
   size_t memory_limit_;
   size_t bytes_allocated_;
   scoped_ptr<base::MemoryPressureListener> memory_pressure_listener_;
   bool enforce_memory_policy_pending_;
   base::WeakPtrFactory<HostDiscardableSharedMemoryManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HostDiscardableSharedMemoryManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_HOST_DISCARDABLE_SHARED_MEMORY_MANAGER_H_