cc: Add image decode queue functionality to image manager.

cc/tiles/decoded_image_tracker.cc

+// Copyright 2016 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 "cc/tiles/decoded_image_tracker.h"
+
+namespace cc {
+namespace {
+const int kNumFramesToLock = 2;
+}  // namespace
+
+DecodedImageTracker::DecodedImageTracker() = default;
+DecodedImageTracker::~DecodedImageTracker() {
+  for (auto& pair : locked_images_)
+    image_controller_->UnlockImageDecode(pair.first);
+}
+
+void DecodedImageTracker::QueueImageDecode(sk_sp<const SkImage> image,
+                                           const base::Closure& callback) {
+  DCHECK(image_controller_);
+  // Queue the decode in the image controller, but switch out the callback for
+  // our own.
+  image_controller_->QueueImageDecode(
+      std::move(image), base::Bind(&DecodedImageTracker::ImageDecodeFinished,
+                                   base::Unretained(this), callback));
+}
+
+void DecodedImageTracker::NotifyFrameFinished() {
+  // Go through the images and if the frame ref count goes to 0, unlock the
+  // image in the controller.
+  for (auto it = locked_images_.begin(); it != locked_images_.end();) {
+    auto id = it->first;
+    int& ref_count = it->second;
+    if (--ref_count != 0) {
+      ++it;
+      continue;
+    }
+    image_controller_->UnlockImageDecode(id);
+    it = locked_images_.erase(it);
+  }
+}
+
+void DecodedImageTracker::ImageDecodeFinished(
+    const base::Closure& callback,
+    ImageController::ImageDecodeRequestId id) {
+  locked_images_.push_back(std::make_pair(id, kNumFramesToLock));
+  callback.Run();
+}
+
+}  // namespace cc