skia: Added chrome implementation of SkDiscardableMemory.

skia/ext/sk_discardable_memory_chrome.h

+// Copyright (c) 2013 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 SKIA_EXT_SK_DISCARDABLE_MEMORY_CHROME_H_
+#define SKIA_EXT_SK_DISCARDABLE_MEMORY_CHROME_H_
+
+#include "base/memory/discardable_memory.h"
+#include "base/memory/singleton.h"
+#include "third_party/skia/src/core/SkDiscardableMemory.h"
+
+namespace skia {
+
+// This class implements the SkDiscardableMemory interface using
+// base::DiscardableMemory.
+class SK_API SkDiscardableMemoryChrome : public SkDiscardableMemory {

[nduca, 2013/08/14 22:53:37]

Also impl is a useful suffix when you're implementign an interface and not in cc
code (where we are insane).

It could be SkDiscardableMemoryImpl sk_discardable_memory_impl.h

and then have a separate file for the factory_impl.

[ernstm, 2013/08/15 20:30:12]

Following the embedding pattern of SkThread, I kept the name
SkDiscardableMemoryChrome and named the files SkDiscardableMemory_chrome.*

+public:
+  SkDiscardableMemoryChrome();

[scroggo, 2013/08/15 14:15:25]

It looks like someone could create an SkDiscardableMemoryChrome directly (rather
than using the factory), and call InitializeAndLock as desired? Is this
intentional?

[ernstm, 2013/08/15 20:30:12]

I think it's safe to create and initialize SkDiscardableMemoryChrome directly,
as the factory was not doing any book keeping (it was now replaced by a
function).

+
+  // Initialize the SkDiscardableMemoryChrome object and lock the memory.
+  // Returns true on success. No memory is allocated if this call returns
+  // false. This call should only be called once.
+  bool InitializeAndLock(size_t bytes);
+
+  // Implementation of SkDiscardableMemory interface.
+  bool lock();
+  void* data();
+  void unlock();
+
+private:
+  scoped_ptr<base::DiscardableMemory> discardable_;
+};
+
+// This singleton class implements the SkDiscardableMemoryFactory interface
+// for creation of SkDiscardableMemoryChrome objects.
+class SK_API SkDiscardableMemoryFactoryChrome
+    : public SkDiscardableMemoryFactory {
+public:
+  static SkDiscardableMemoryFactoryChrome* GetInstance() {
+    return Singleton<SkDiscardableMemoryFactoryChrome>::get();
+  }
+
+  // Implementation of SkDiscardableMemoryFactory interface.
+  SkDiscardableMemory* create(size_t bytes);
+
+private:
+  SkDiscardableMemoryFactoryChrome() {}
+  friend struct DefaultSingletonTraits<SkDiscardableMemoryFactoryChrome>;
+};
+
+}  // namespace skia
+
+#endif  // SKIA_EXT_SK_DISCARDABLE_MEMORY_CHROME_H_