[Not for review] Discardable memory emulation

content/renderer/render_process_discardable_memory_provider.h

+// Copyright (c) 2012 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.
+
+#include "base/hash_tables.h"
+#include "base/memory/discardable_memory.h"
+#include "content/common/content_export.h"
+#include "content/renderer/render_process_visibility_manager.h"
+
+#if defined(COMPILER_GCC)
+namespace base { class DiscardableMemory; }
+
+namespace BASE_HASH_NAMESPACE {
+template <>
+struct hash<const base::DiscardableMemory*> {
+  size_t operator()(const base::DiscardableMemory* ptr) const {
+    return hash<size_t>()(reinterpret_cast<size_t>(ptr));
+  }
+};
+}  // namespace BASE_HASH_NAMESPACE
+#endif  // COMPILER
+
+namespace content {
+
+class CONTENT_EXPORT RenderProcessDiscardableMemoryProvider
+    : public base::DiscardableMemoryProvider,
+      public RenderProcessVisibilityObserver {
+ public:
+  RenderProcessDiscardableMemoryProvider();
+  virtual ~RenderProcessDiscardableMemoryProvider();
+
+  bool Register(const base::DiscardableMemory* discardable, size_t size);
+  void Unregister(const base::DiscardableMemory* discardable);
+  base::LockDiscardableMemoryStatus Lock(
+      const base::DiscardableMemory* discardable);
+  void Unlock(const base::DiscardableMemory* discardable);
+  void* Memory(const base::DiscardableMemory* discardable) const;
+
+ private:
+  struct AllocatedMemory {
+    void* memory;
+    bool locked;
+    size_t size;
+  };
+
+  // RenderProcessVisibilityObserver implementation.
+  virtual void RenderProcessVisibilityChanged(bool visible) OVERRIDE;
+
+  // DiscardableMemoryProvider implementation.
+  virtual base::DiscardableMemory* CreateDiscardableMemory() OVERRIDE;
+  virtual bool PurgeForTestingSupported() const OVERRIDE;
+  virtual void PurgeForTesting() OVERRIDE;
+
+  void Purge();
+  void EnforcePolicy();
+
+  typedef
+      base::hash_map<const base::DiscardableMemory*, AllocatedMemory>
+      AllocationMap;
+
+  AllocationMap allocations_;
+  bool visible_;
+
+  DISALLOW_COPY_AND_ASSIGN(RenderProcessDiscardableMemoryProvider);
+};
+
+}  // namespace content