cc: Add checker-imaging support to TileManager.

cc/tiles/checker_image_tracker.h

+// Copyright 2017 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 CC_TILES_CHECKER_IMAGE_TRACKER_H_
+#define CC_TILES_CHECKER_IMAGE_TRACKER_H_
+
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "cc/playback/image_id.h"
+#include "cc/tiles/image_controller.h"
+#include "third_party/skia/include/core/SkImage.h"
+
+namespace cc {
+
+class CheckerImageTrackerClient {
+ public:
+  virtual ~CheckerImageTrackerClient() {}

[vmpstr, 2017/02/10 19:25:42]

= default

[Khushal, 2017/02/10 22:09:19]

Done.

+
+  virtual void NeedsInvalidationForCheckerImagedTiles() = 0;
+};
+
+class CheckerImageTracker {
+ public:
+  CheckerImageTracker(ImageController* image_controller,
+                      CheckerImageTrackerClient* client,
+                      bool enable_checker_imaging);
+  ~CheckerImageTracker();
+
+  // Given the |images| for a tile, filters the images which will be deferred
+  // asynchronously using the image decoded service, eliminating them from
+  // |images| adds them to the |checkered_images| set, so they can be skipped
+  // during the rasterization of this tile.
+  // The entries remaining in |images| are for images for which a cached decode
+  // from the image decode service is available, or which must be decoded before
+  // before this tile can be rasterized.
+  void FilterImagesForCheckeringForTile(
+      std::vector<DrawImage>* images,
+      std::unordered_set<ImageId>* checkered_images,
+      WhichTree tree);
+
+  // Returns the set of images to invalidate on the sync tree.
+  const std::unordered_set<ImageId>& TakeImagesToInvalidateOnSyncTree();

[vmpstr, 2017/02/10 19:25:42]

vector? Also "take" function should probably return a value, not a reference.
Internally I think you'd want to use std::move(member_); or something to that
effect.

[Khushal, 2017/02/10 22:09:19]

I'll have to copy to return a value. We have to internally keep a copy until the
sync tree is activated so can't move that.

+
+  void DidActivateSyncTree();
+
+ private:
+  void DidFinishImageDecode(ImageId image_id,
+                            ImageController::ImageDecodeRequestId request_id);
+
+  // Returns true if the decode for |image| will be deferred to the image decode
+  // service and it should be be skipped during raster.
+  bool ShouldCheckerImage(const sk_sp<const SkImage> image,
+                          WhichTree tree) const;
+
+  void ScheduleImageDecodeIfNecessary(const sk_sp<const SkImage> image);
+
+  ImageController* image_controller_;

[vmpstr, 2017/02/10 19:25:42]

It's very nice that these three lines align on the right. Good job. :P

[Khushal, 2017/02/10 22:09:19]

I'm glad you noticed. :P

+  CheckerImageTrackerClient* client_;
+  const bool enable_checker_imaging_;
+
+  using ImageIdSet = std::unordered_set<ImageId>;
+
+  // A set of images which have been decoded and are pending invalidation for
+  // raster on the checkered tiles.
+  ImageIdSet images_pending_invalidation_;
+
+  // A set of images which were invalidated on the current sync tree.
+  ImageIdSet invalidated_images_on_current_sync_tree_;
+
+  // A set of images which are currently pending decode from the image decode
+  // service.
+  // TODO(khushalsagar): This should be a queue that gets re-built each time we
+  // do a PrepareTiles? See crbug.com/689184.
+  ImageIdSet pending_image_decodes_;
+
+  // A set of images which have been decoded at least once from the
+  // ImageDecodeService and should not be checkered again.
+  ImageIdSet images_decoded_once_;

[vmpstr, 2017/02/10 19:25:42]

Can you file a TODO here. I think we might be able to do an optimization here
eventually where we basically say "any id lower than X can be considered decoded
once, and anything above X, you can check this set". This is so that we still
try and retain a reasonable bound on the size of this set.

[Khushal, 2017/02/10 22:09:19]

Hmmm, we'll have to see how feasible it would be to do this approach. Do we do
this only if all entries below a certain id are in this set so they can be
pruned out? We only store ids for images decoded using the image decode service
here so we may not see all the ids here.

+
+  // A map of image id to image decode request id for images to be unlocked.
+  std::unordered_map<ImageId, ImageController::ImageDecodeRequestId>
+      image_id_to_decode_request_id_;
+
+  base::WeakPtrFactory<CheckerImageTracker> weak_factory_;
+};
+
+}  // namespace cc
+
+#endif  // CC_TILES_CHECKER_IMAGE_TRACKER_H_