cc: Add a flag to check for tile priority inversion in AssignGpuMemory.

cc/tiles/tile_manager.cc

Index: cc/tiles/tile_manager.cc
diff --git a/cc/tiles/tile_manager.cc b/cc/tiles/tile_manager.cc
index 0c15378545f86b7d9e6b14bc954e6ae3ee99e63b..425cfe8cc7f0d2bd7d89ab2ca66770083eca35b6 100644
--- a/cc/tiles/tile_manager.cc
+++ b/cc/tiles/tile_manager.cc
@@ -345,7 +345,8 @@ RasterTaskCompletionStatsAsValue(const RasterTaskCompletionStats& stats) {
 TileManager::TileManager(TileManagerClient* client,
                          base::SequencedTaskRunner* task_runner,
                          size_t scheduled_raster_task_limit,
-                         bool use_partial_raster)
+                         bool use_partial_raster,
+                         bool check_tile_priority_inversion)
     : client_(client),
       task_runner_(task_runner),
       resource_pool_(nullptr),
@@ -366,6 +367,7 @@ TileManager::TileManager(TileManagerClient* client,
       has_scheduled_tile_tasks_(false),
       prepare_tiles_count_(0u),
       next_tile_id_(0u),
+      check_tile_priority_inversion_(check_tile_priority_inversion),
       task_set_finished_weak_ptr_factory_(this) {}
 
 TileManager::~TileManager() {
@@ -753,6 +755,41 @@ TileManager::PrioritizedWorkToSchedule TileManager::AssignGpuMemoryToTiles() {
       tile->draw_info().set_was_a_prepaint_tile();
   }
 
+  // Debugging to check that remaining tiles in the priority queue are not in
+  // the NOW bin and are required for neither activation nor draw.
+  // This runs if the following conditions hold:
+  //  - check_tile_priority_inversion has been enabled.
+  //  - the loop above has processed all tiles that would be needed for any
+  //    signals to fire (that is,
+  //    all_tiles_that_need_to_be_rasterized_are_scheduled_ is true)
+  //  - Memory limit policy allows for any tiles to be scheduled at all (ie it's
+  //    not ALLOW_NOTHING).
+  if (check_tile_priority_inversion_ &&
+      all_tiles_that_need_to_be_rasterized_are_scheduled_ &&
+      global_state_.memory_limit_policy != ALLOW_NOTHING) {
+    TilePriority::PriorityBin highest_bin_found = TilePriority::NOW;
+    for (; !raster_priority_queue->IsEmpty(); raster_priority_queue->Pop()) {
+      const PrioritizedTile& prioritized_tile = raster_priority_queue->Top();
+      Tile* tile = prioritized_tile.tile();
+      TilePriority priority = prioritized_tile.priority();
+
+      if (priority.priority_bin > highest_bin_found)
+        highest_bin_found = priority.priority_bin;
+
+      CHECK_NE(TilePriority::NOW, priority.priority_bin)
+          << "mode: " << global_state_.tree_priority
+          << " highest bin: " << highest_bin_found;
+      CHECK(!tile->required_for_activation())
+          << "mode: " << global_state_.tree_priority
+          << " bin: " << priority.priority_bin
+          << " highest bin: " << highest_bin_found;
+      CHECK(!tile->required_for_draw())
+          << "mode: " << global_state_.tree_priority
+          << " bin: " << priority.priority_bin
+          << " highest bin: " << highest_bin_found;
+    }
+  }
+
   // Note that we should try and further reduce memory in case the above loop
   // didn't reduce memory. This ensures that we always release as many resources
   // as possible to stay within the memory limit.