cc: Add checker-imaging support to TileManager.

cc/playback/image_id.h

Index: cc/playback/image_id.h
diff --git a/cc/playback/image_id.h b/cc/playback/image_id.h
index c29810b6746dc961d545d0dca387793b00b8c951..69a8610e237e907e041784aabc160738cfb07370 100644
--- a/cc/playback/image_id.h
+++ b/cc/playback/image_id.h
@@ -5,9 +5,16 @@
 #ifndef CC_PLAYBACK_IMAGE_ID_H_
 #define CC_PLAYBACK_IMAGE_ID_H_
 
+#include <stdint.h>
+#include <unordered_set>
+
+#include "base/containers/flat_set.h"
+
 namespace cc {
 
 using ImageId = uint32_t;
+using ImageIdSet = std::unordered_set<ImageId>;
+using ImageIdFlatSet = base::flat_set<ImageId>;

[vmpstr, 2017/02/13 22:49:30]

I don't really like that we have both an unordered set and a flat set.
Especially since we have to name the typedef as ImageIdFlatSet, which needlessly
reveals the underlying type. Remind me, why do we need ImageIdSet? Can we just
keep the flat_set version and name it ImageIdSet?

[Khushal, 2017/02/14 05:10:22]

We were using the unordered_set for the internal state in the tracker, like the
once decoded images set, where using a flat set will become sub-optimal.

 
 }  // namespace cc