cc: Add TileManager::GetActivationStateAsValue for debugging state.

cc/tiles/tile_manager.h

Index: cc/tiles/tile_manager.h
diff --git a/cc/tiles/tile_manager.h b/cc/tiles/tile_manager.h
index 5de0a15485a61a511906fa1552354f07d906643d..3327cf1bf99347fc75076ed1394eeacc7f980176 100644
--- a/cc/tiles/tile_manager.h
+++ b/cc/tiles/tile_manager.h
@@ -229,6 +229,11 @@ class CC_EXPORT TileManager : CheckerImageTrackerClient {
   // CheckerImageTrackerClient implementation.
   void NeedsInvalidationForCheckerImagedTiles() override;
 
+  // This method can only be used for debugging information, since it performs a
+  // non trivial amount of work.
+  std::unique_ptr<base::trace_event::ConvertableToTraceFormat>
+  ActivationStateAsValue();
+
  protected:
   friend class Tile;
   // Must be called by tile during destruction.