base: Refactor DiscardableMemoryManager for use with different type of allocations.

base/memory/discardable_memory_allocation.h

Index: base/memory/discardable_memory_allocation.h
diff --git a/base/memory/discardable_memory_allocation.h b/base/memory/discardable_memory_allocation.h
new file mode 100644
index 0000000000000000000000000000000000000000..98e8b98bbd86ff6c7f5cbee311a4a392a9b4dc3b
--- /dev/null
+++ b/base/memory/discardable_memory_allocation.h
@@ -0,0 +1,41 @@
+// 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_ALLOCATION_H_
+#define BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATION_H_
+
+#include "base/base_export.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace base {
+namespace internal {
+
+class BASE_EXPORT_PRIVATE DiscardableMemoryAllocation {

[willchan no longer on Chromium, 2014/04/01 01:11:08]

Can you comment this class so it's obvious how this relates to the other classes
here? Or having a link to another file with some central comment about the
overall architecture here would be helpful. There are enough layers now that
they keep getting paged out of my head and I have to swap them back in.

[reveman, 2014/04/03 17:02:12]

Added a comment here and improved the comments in _manager.h so they better
explain how all this fits together.

+ public:
+  class BASE_EXPORT_PRIVATE Factory {
+   public:
+    virtual scoped_ptr<DiscardableMemoryAllocation> CreateLockedAllocation(
+        size_t bytes) = 0;
+
+   protected:
+    virtual ~Factory() {}
+  };
+
+  virtual ~DiscardableMemoryAllocation() {}
+
+  // Locks the allocation so that it will not be purged by the system. Returns
+  // true if memory is still resident.
+  virtual bool Lock() = 0;
+
+  // Unlocks the allocation so that it can be purged by the system.
+  virtual void Unlock() = 0;
+
+  // Returns the memory address for this allocation.
+  virtual void* Memory() = 0;
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_MEMORY_DISCARDABLE_MEMORY_ALLOCATION_H_