skia: Added chrome implementation of SkDiscardableMemory.

skia/ext/SkDiscardableMemory_chrome.cc

+// 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.
+
+#include "SkDiscardableMemory_chrome.h"
+
+SkDiscardableMemoryChrome::SkDiscardableMemoryChrome()
+    : discardable_(new base::DiscardableMemory()) {
+}
+
+bool SkDiscardableMemoryChrome::lock() {
+  base::LockDiscardableMemoryStatus status = discardable_->Lock();
+  switch (status) {
+    case base::DISCARDABLE_MEMORY_SUCCESS:
+      return true;
+    case base::DISCARDABLE_MEMORY_PURGED:
+      discardable_->Unlock();
+      return false;

[Ian Vollick, 2013/08/16 11:36:31]

Do you really want to do this in response to being purged? Although you'll need
to recreate the data, you've got your memory locked and allocated and ready to
go at this point.

+    default:
+      discardable_.reset();
+      return false;
+  }
+}
+
+void* SkDiscardableMemoryChrome::data() {
+  return discardable_->Memory();
+}
+
+void SkDiscardableMemoryChrome::unlock() {
+  discardable_->Unlock();
+}
+
+bool SkDiscardableMemoryChrome::InitializeAndLock(size_t bytes) {
+  return discardable_->InitializeAndLock(bytes);
+}
+
+SkDiscardableMemory* SkDiscardableMemory::Create(size_t bytes) {
+  if (!base::DiscardableMemory::Supported()) {
+    return NULL;
+  }
+  scoped_ptr<SkDiscardableMemoryChrome> discardable(
+      new SkDiscardableMemoryChrome());
+  if (discardable->InitializeAndLock(bytes))
+    return discardable.release();
+  return NULL;
+}