cc: Remove tile sharing from tilings.

cc/resources/picture_layer_tiling.cc

Index: cc/resources/picture_layer_tiling.cc
diff --git a/cc/resources/picture_layer_tiling.cc b/cc/resources/picture_layer_tiling.cc
index 51c8ca735c1b908e410dfc1cc32625fa944727f7..30a73b8e8dbf1e47e6332878a0d18810512a4518 100644
--- a/cc/resources/picture_layer_tiling.cc
+++ b/cc/resources/picture_layer_tiling.cc
@@ -79,8 +79,6 @@ PictureLayerTiling::PictureLayerTiling(
 }
 
 PictureLayerTiling::~PictureLayerTiling() {
-  for (TileMap::const_iterator it = tiles_.begin(); it != tiles_.end(); ++it)
-    it->second->set_shared(false);
 }
 
 // static
@@ -94,13 +92,7 @@ float PictureLayerTiling::CalculateSoonBorderDistance(
       max_dimension * kSoonBorderDistanceViewportPercentage);
 }
 
-Tile* PictureLayerTiling::CreateTile(int i,
-                                     int j,
-                                     const PictureLayerTiling* twin_tiling,
-                                     PictureLayerTiling* recycled_twin) {
-  // Can't have both a (pending or active) twin and a recycled twin tiling.
-  DCHECK_IMPLIES(twin_tiling, !recycled_twin);
-  DCHECK_IMPLIES(recycled_twin, !twin_tiling);
+Tile* PictureLayerTiling::CreateTile(int i, int j) {
   TileMapKey key(i, j);
   DCHECK(tiles_.find(key) == tiles_.end());
 
@@ -108,116 +100,73 @@ Tile* PictureLayerTiling::CreateTile(int i,
   gfx::Rect tile_rect = paint_rect;
   tile_rect.set_size(tiling_data_.max_texture_size());
 
-  // Check our twin for a valid tile.
-  if (twin_tiling &&
-      tiling_data_.max_texture_size() ==
-      twin_tiling->tiling_data_.max_texture_size()) {
-    if (Tile* candidate_tile = twin_tiling->TileAt(i, j)) {
-      gfx::Rect rect =
-          gfx::ScaleToEnclosingRect(paint_rect, 1.0f / contents_scale_);
-      const Region* invalidation = client_->GetPendingInvalidation();
-      if (!invalidation || !invalidation->Intersects(rect)) {
-        DCHECK(!candidate_tile->is_shared());
-        DCHECK_EQ(i, candidate_tile->tiling_i_index());
-        DCHECK_EQ(j, candidate_tile->tiling_j_index());
-        candidate_tile->set_shared(true);
-        tiles_[key] = candidate_tile;
-        return candidate_tile;
-      }
-    }
-  }
-
   if (!raster_source_->CoversRect(tile_rect, contents_scale_))
     return nullptr;
 
-  // Create a new tile because our twin didn't have a valid one.
   scoped_refptr<Tile> tile = client_->CreateTile(contents_scale_, tile_rect);
-  DCHECK(!tile->is_shared());
   tile->set_tiling_index(i, j);
   tiles_[key] = tile;
-
-  if (recycled_twin) {
-    DCHECK(recycled_twin->tiles_.find(key) == recycled_twin->tiles_.end());
-    // Do what recycled_twin->CreateTile() would do.
-    tile->set_shared(true);
-    recycled_twin->tiles_[key] = tile;
-  }
   return tile.get();
 }
 
 void PictureLayerTiling::CreateMissingTilesInLiveTilesRect() {
-  const PictureLayerTiling* twin_tiling =
-      client_->GetPendingOrActiveTwinTiling(this);
-  // There is no recycled twin during commit from the main thread which is when
-  // this occurs.
-  PictureLayerTiling* null_recycled_twin = nullptr;
-  DCHECK_EQ(null_recycled_twin, client_->GetRecycledTwinTiling(this));
   bool include_borders = false;
-  for (TilingData::Iterator iter(
-           &tiling_data_, live_tiles_rect_, include_borders);
-       iter;
-       ++iter) {
+  for (TilingData::Iterator iter(&tiling_data_, live_tiles_rect_,
+                                 include_borders);
+       iter; ++iter) {
     TileMapKey key = iter.index();
     TileMap::iterator find = tiles_.find(key);
     if (find != tiles_.end())
       continue;
-    CreateTile(key.first, key.second, twin_tiling, null_recycled_twin);
-  }
 
+    if (ShouldCreateTileAt(key.first, key.second))
+      CreateTile(key.first, key.second);
+  }
   VerifyLiveTilesRect(false);
 }
 
-void PictureLayerTiling::CloneTilesAndPropertiesFrom(
-    const PictureLayerTiling& twin_tiling) {
-  DCHECK_EQ(&twin_tiling, client_->GetPendingOrActiveTwinTiling(this));
+void PictureLayerTiling::TakeTilesAndPropertiesFrom(
+    PictureLayerTiling* pending_twin,
+    const Region& layer_invalidation) {
+  TRACE_EVENT0("cc", "TakeTilesAndPropertiesFrom");
+  SetRasterSourceAndResize(pending_twin->raster_source_);
 
-  SetRasterSourceAndResize(twin_tiling.raster_source_);
-  DCHECK_EQ(twin_tiling.contents_scale_, contents_scale_);
-  DCHECK_EQ(twin_tiling.raster_source_, raster_source_);
-  DCHECK_EQ(twin_tiling.tile_size().ToString(), tile_size().ToString());
+  RemoveTilesInRegion(layer_invalidation, false /* recreate tiles */);
 
-  resolution_ = twin_tiling.resolution_;
+  for (TileMap::value_type& tile_pair : tiles_)
+    tile_pair.second->set_raster_source(raster_source_.get());
 
-  SetLiveTilesRect(twin_tiling.live_tiles_rect());
-
-  // Recreate unshared tiles.
-  std::vector<TileMapKey> to_remove;
-  for (const auto& tile_map_pair : tiles_) {
-    TileMapKey key = tile_map_pair.first;
-    Tile* tile = tile_map_pair.second.get();
-    if (!tile->is_shared())
-      to_remove.push_back(key);
-  }
-  // The recycled twin does not exist since there is a pending twin (which is
-  // |twin_tiling|).
-  PictureLayerTiling* null_recycled_twin = nullptr;
-  DCHECK_EQ(null_recycled_twin, client_->GetRecycledTwinTiling(this));
-  for (const auto& key : to_remove) {
-    RemoveTileAt(key.first, key.second, null_recycled_twin);
-    CreateTile(key.first, key.second, &twin_tiling, null_recycled_twin);
+  resolution_ = pending_twin->resolution_;
+  bool create_missing_tiles = false;
+  if (live_tiles_rect_.IsEmpty()) {
+    live_tiles_rect_ = pending_twin->live_tiles_rect();
+    create_missing_tiles = true;
+  } else {
+    SetLiveTilesRect(pending_twin->live_tiles_rect());
   }
 
-  // Create any missing tiles from the |twin_tiling|.
-  for (const auto& tile_map_pair : twin_tiling.tiles_) {
-    TileMapKey key = tile_map_pair.first;
-    Tile* tile = tile_map_pair.second.get();
-    if (!tile->is_shared())
-      CreateTile(key.first, key.second, &twin_tiling, null_recycled_twin);
+  if (tiles_.size() < pending_twin->tiles_.size()) {
+    tiles_.swap(pending_twin->tiles_);
+    tiles_.insert(pending_twin->tiles_.begin(), pending_twin->tiles_.end());
+  } else {
+    for (TileMap::value_type& tile_pair : pending_twin->tiles_) {
+      tiles_[tile_pair.first].swap(tile_pair.second);
+      DCHECK(tiles_[tile_pair.first]->raster_source() == raster_source_.get());
+    }
   }
+  pending_twin->tiles_.clear();
+
+  if (create_missing_tiles)
+    CreateMissingTilesInLiveTilesRect();
 
-  DCHECK_EQ(twin_tiling.tiles_.size(), tiles_.size());
-#if DCHECK_IS_ON()
-  for (const auto& tile_map_pair : tiles_)
-    DCHECK(tile_map_pair.second->is_shared());
   VerifyLiveTilesRect(false);
-#endif
 
-  UpdateTilePriorityRects(twin_tiling.current_content_to_screen_scale_,
-                          twin_tiling.current_visible_rect_,
-                          twin_tiling.current_skewport_rect_,
-                          twin_tiling.current_soon_border_rect_,
-                          twin_tiling.current_eventually_rect_,
-                          twin_tiling.current_occlusion_in_layer_space_);
+  SetTilePriorityRects(pending_twin->current_content_to_screen_scale_,
+                       pending_twin->current_visible_rect_,
+                       pending_twin->current_skewport_rect_,
+                       pending_twin->current_soon_border_rect_,
+                       pending_twin->current_eventually_rect_,
+                       pending_twin->current_occlusion_in_layer_space_);
 }
 
 void PictureLayerTiling::SetRasterSourceAndResize(
@@ -270,36 +219,42 @@ void PictureLayerTiling::SetRasterSourceAndResize(
 
   // There is no recycled twin since this is run on the pending tiling
   // during commit, and on the active tree during activate.
-  PictureLayerTiling* null_recycled_twin = nullptr;
-  DCHECK_EQ(null_recycled_twin, client_->GetRecycledTwinTiling(this));
-
   // Drop tiles outside the new layer bounds if the layer shrank.
   for (int i = after_right + 1; i <= before_right; ++i) {
     for (int j = before_top; j <= before_bottom; ++j)
-      RemoveTileAt(i, j, null_recycled_twin);
+      RemoveTileAt(i, j);
   }
   for (int i = before_left; i <= after_right; ++i) {
     for (int j = after_bottom + 1; j <= before_bottom; ++j)
-      RemoveTileAt(i, j, null_recycled_twin);
+      RemoveTileAt(i, j);
   }
 
-  // If the layer grew, the live_tiles_rect_ is not changed, but a new row
-  // and/or column of tiles may now exist inside the same live_tiles_rect_.
-  const PictureLayerTiling* twin_tiling =
-      client_->GetPendingOrActiveTwinTiling(this);
   if (after_right > before_right) {
     DCHECK_EQ(after_right, before_right + 1);
-    for (int j = before_top; j <= after_bottom; ++j)
-      CreateTile(after_right, j, twin_tiling, null_recycled_twin);
+    for (int j = before_top; j <= after_bottom; ++j) {
+      if (ShouldCreateTileAt(after_right, j))
+        CreateTile(after_right, j);
+    }
   }
   if (after_bottom > before_bottom) {
     DCHECK_EQ(after_bottom, before_bottom + 1);
-    for (int i = before_left; i <= before_right; ++i)
-      CreateTile(i, after_bottom, twin_tiling, null_recycled_twin);
+    for (int i = before_left; i <= before_right; ++i) {
+      if (ShouldCreateTileAt(i, after_bottom))
+        CreateTile(i, after_bottom);
+    }
   }
 }
 
 void PictureLayerTiling::Invalidate(const Region& layer_invalidation) {
+  DCHECK_IMPLIES(client_->GetTree() == ACTIVE_TREE,
+                 !client_->GetPendingOrActiveTwinTiling(this));
+  RemoveTilesInRegion(layer_invalidation, true /* recreate tiles */);
+}
+
+void PictureLayerTiling::RemoveTilesInRegion(const Region& layer_invalidation,
+                                             bool recreate_tiles) {
+  // We only invalidate the active tiling when it's orphaned: it has no pending
+  // twin, so it's slated for removal in the future.
   if (live_tiles_rect_.IsEmpty())
     return;
   std::vector<TileMapKey> new_tile_keys;
@@ -323,41 +278,82 @@ void PictureLayerTiling::Invalidate(const Region& layer_invalidation) {
     // Since the content_rect includes border pixels already, don't include
     // borders when iterating to avoid double counting them.
     bool include_borders = false;
-    for (TilingData::Iterator iter(
-             &tiling_data_, content_rect, include_borders);
-         iter;
-         ++iter) {
-      // There is no recycled twin for the pending tree during commit, or for
-      // the active tree during activation.
-      PictureLayerTiling* null_recycled_twin = nullptr;
-      DCHECK_EQ(null_recycled_twin, client_->GetRecycledTwinTiling(this));
-      if (RemoveTileAt(iter.index_x(), iter.index_y(), null_recycled_twin))
-        new_tile_keys.push_back(iter.index());
+    for (
+        TilingData::Iterator iter(&tiling_data_, content_rect, include_borders);
+        iter; ++iter) {
+      if (RemoveTileAt(iter.index_x(), iter.index_y())) {
+        if (recreate_tiles)
+          new_tile_keys.push_back(iter.index());
+      }
     }
   }
 
-  if (!new_tile_keys.empty()) {
-    // During commit from the main thread, invalidations can never be shared
-    // with the active tree since the active tree has different content there.
-    // And when invalidating an active-tree tiling, it means there was no
-    // pending tiling to clone from.
-    const PictureLayerTiling* null_twin_tiling = nullptr;
-    PictureLayerTiling* null_recycled_twin = nullptr;
-    DCHECK_EQ(null_recycled_twin, client_->GetRecycledTwinTiling(this));
-    for (size_t i = 0; i < new_tile_keys.size(); ++i) {
-      CreateTile(new_tile_keys[i].first, new_tile_keys[i].second,
-                 null_twin_tiling, null_recycled_twin);
-    }
-  }
+  for (const auto& key : new_tile_keys)
+    CreateTile(key.first, key.second);
 }
 
 void PictureLayerTiling::SetRasterSourceOnTiles() {
-  // Shared (ie. non-invalidated) tiles on the pending tree are updated to use
-  // the new raster source. When this raster source is activated, the raster
-  // source will remain valid for shared tiles in the active tree.
-  for (TileMap::const_iterator it = tiles_.begin(); it != tiles_.end(); ++it)
-    it->second->set_raster_source(raster_source_);
-  VerifyLiveTilesRect(false);
+  if (client_->GetTree() == PENDING_TREE)
+    return;
+
+  for (TileMap::value_type& tile_pair : tiles_)
+    tile_pair.second->set_raster_source(raster_source_.get());
+}
+
+bool PictureLayerTiling::ShouldCreateTileAt(int i, int j) const {
+  // Active tree should always create a tile. The reason for this is that active
+  // tree represents content that we draw on screen, which means that whenever
+  // we check whether a tile should exist somewhere, the answer is yes. This
+  // doesn't mean it will actually be created (if raster source doesn't cover
+  // the tile for instance). Pending tree, on the other hand, should only be
+  // creating tiles that are different from the current active tree, which is
+  // represented by the logic in the rest of the function.
+  if (client_->GetTree() == ACTIVE_TREE)
+    return true;
+
+  // If the pending tree has no active twin, then it needs to create all tiles.
+  const PictureLayerTiling* active_twin =
+      client_->GetPendingOrActiveTwinTiling(this);
+  if (!active_twin)
+    return true;
+
+  // Pending tree will override the entire active tree if indices don't match.
+  if (!TilingMatchesTileIndices(active_twin))
+    return true;
+
+  gfx::Rect paint_rect = tiling_data_.TileBoundsWithBorder(i, j);
+  gfx::Rect tile_rect = paint_rect;
+  tile_rect.set_size(tiling_data_.max_texture_size());
+
+  // If the active tree can't create a tile, because of its raster source, then
+  // the pending tree should create one.
+  if (!active_twin->raster_source()->CoversRect(tile_rect, contents_scale()))
+    return true;
+
+  const Region* layer_invalidation = client_->GetPendingInvalidation();
+  gfx::Rect layer_rect =
+      gfx::ScaleToEnclosingRect(tile_rect, 1.f / contents_scale());
+
+  // If this tile is invalidated, then the pending tree should create one.
+  if (layer_invalidation && layer_invalidation->Intersects(layer_rect))
+    return true;
+
+  // If the active tree doesn't have a tile here, but it's in the pending tree's
+  // visible rect, then the pending tree should create a tile. This can happen
+  // if the pending visible rect is outside of the active tree's live tiles
+  // rect. In those situations, we need to block activation until we're ready to
+  // display content, which will have to come from the pending tree.
+  if (!active_twin->TileAt(i, j) && current_visible_rect_.Intersects(tile_rect))
+    return true;
+
+  // In all other cases, the pending tree doesn't need to create a tile.
+  return false;
+}
+
+bool PictureLayerTiling::TilingMatchesTileIndices(
+    const PictureLayerTiling* twin) const {
+  return tiling_data_.max_texture_size() ==
+         twin->tiling_data_.max_texture_size();
 }
 
 PictureLayerTiling::CoverageIterator::CoverageIterator()
@@ -499,29 +495,16 @@ gfx::RectF PictureLayerTiling::CoverageIterator::texture_rect() const {
   return texture_rect;
 }
 
-bool PictureLayerTiling::RemoveTileAt(int i,
-                                      int j,
-                                      PictureLayerTiling* recycled_twin) {
+bool PictureLayerTiling::RemoveTileAt(int i, int j) {
   TileMap::iterator found = tiles_.find(TileMapKey(i, j));
   if (found == tiles_.end())
     return false;
-  found->second->set_shared(false);
   tiles_.erase(found);
-  if (recycled_twin) {
-    // Recycled twin does not also have a recycled twin, so pass null.
-    recycled_twin->RemoveTileAt(i, j, nullptr);
-  }
   return true;
 }
 
 void PictureLayerTiling::Reset() {
   live_tiles_rect_ = gfx::Rect();
-  PictureLayerTiling* recycled_twin = client_->GetRecycledTwinTiling(this);
-  for (TileMap::const_iterator it = tiles_.begin(); it != tiles_.end(); ++it) {
-    it->second->set_shared(false);
-    if (recycled_twin)
-      recycled_twin->RemoveTileAt(it->first.first, it->first.second, nullptr);
-  }
   tiles_.clear();
 }
 
@@ -631,14 +614,14 @@ bool PictureLayerTiling::ComputeTilePriorityRects(
                            visible_rect_in_content_space);
   last_viewport_in_layer_space_ = viewport_in_layer_space;
 
+  SetTilePriorityRects(content_to_screen_scale, visible_rect_in_content_space,
+                       skewport, soon_border_rect, eventually_rect,
+                       occlusion_in_layer_space);
   SetLiveTilesRect(eventually_rect);
-  UpdateTilePriorityRects(
-      content_to_screen_scale, visible_rect_in_content_space, skewport,
-      soon_border_rect, eventually_rect, occlusion_in_layer_space);
   return true;
 }
 
-void PictureLayerTiling::UpdateTilePriorityRects(
+void PictureLayerTiling::SetTilePriorityRects(
     float content_to_screen_scale,
     const gfx::Rect& visible_rect_in_content_space,
     const gfx::Rect& skewport,
@@ -669,36 +652,24 @@ void PictureLayerTiling::SetLiveTilesRect(
   if (live_tiles_rect_ == new_live_tiles_rect)
     return;
 
-  PictureLayerTiling* recycled_twin = client_->GetRecycledTwinTiling(this);
-
   // Iterate to delete all tiles outside of our new live_tiles rect.
-  for (TilingData::DifferenceIterator iter(&tiling_data_,
-                                           live_tiles_rect_,
+  for (TilingData::DifferenceIterator iter(&tiling_data_, live_tiles_rect_,
                                            new_live_tiles_rect);
-       iter;
-       ++iter) {
-    RemoveTileAt(iter.index_x(), iter.index_y(), recycled_twin);
+       iter; ++iter) {
+    RemoveTileAt(iter.index_x(), iter.index_y());
   }
 
-  const PictureLayerTiling* twin_tiling =
-      client_->GetPendingOrActiveTwinTiling(this);
-
   // Iterate to allocate new tiles for all regions with newly exposed area.
-  for (TilingData::DifferenceIterator iter(&tiling_data_,
-                                           new_live_tiles_rect,
+  for (TilingData::DifferenceIterator iter(&tiling_data_, new_live_tiles_rect,
                                            live_tiles_rect_);
-       iter;
-       ++iter) {
+       iter; ++iter) {
     TileMapKey key(iter.index());
-    CreateTile(key.first, key.second, twin_tiling, recycled_twin);
+    if (ShouldCreateTileAt(key.first, key.second))
+      CreateTile(key.first, key.second);
   }
 
   live_tiles_rect_ = new_live_tiles_rect;
   VerifyLiveTilesRect(false);
-  if (recycled_twin) {
-    recycled_twin->live_tiles_rect_ = live_tiles_rect_;
-    recycled_twin->VerifyLiveTilesRect(true);
-  }
 }
 
 void PictureLayerTiling::VerifyLiveTilesRect(bool is_on_recycle_tree) const {
@@ -720,136 +691,126 @@ void PictureLayerTiling::VerifyLiveTilesRect(bool is_on_recycle_tree) const {
         << " tile bounds "
         << tiling_data_.TileBounds(it->first.first, it->first.second).ToString()
         << " live_tiles_rect " << live_tiles_rect_.ToString();
-    DCHECK_IMPLIES(is_on_recycle_tree, it->second->is_shared());
   }
 #endif
 }
 
 bool PictureLayerTiling::IsTileOccluded(const Tile* tile) const {
-  DCHECK(tile);
+  // If this tile is not occluded on this tree, then it is not occluded.
+  if (!IsTileOccludedOnCurrentTree(tile))
+    return false;
+
+  // Otherwise, if this is the pending tree, we're done and the tile is
+  // occluded.
+  if (client_->GetTree() == PENDING_TREE)
+    return true;
+
+  // On the active tree however, we need to check if this tile will be
+  // unoccluded upon activation, in which case it has to be considered
+  // unoccluded.
+  const PictureLayerTiling* pending_twin =
+      client_->GetPendingOrActiveTwinTiling(this);
+  if (pending_twin) {
+    // If there's a pending tile in the same position. Or if the pending twin
+    // would have to be creating all tiles, then we don't need to worry about
+    // occlusion on the twin.
+    if (!TilingMatchesTileIndices(pending_twin) ||
+        pending_twin->TileAt(tile->tiling_i_index(), tile->tiling_j_index())) {
+      return true;
+    }
+    return pending_twin->IsTileOccludedOnCurrentTree(tile);
+  }
+  return true;
+}
 
+bool PictureLayerTiling::IsTileOccludedOnCurrentTree(const Tile* tile) const {
   if (!current_occlusion_in_layer_space_.HasOcclusion())
     return false;
-
   gfx::Rect tile_query_rect =
       gfx::IntersectRects(tile->content_rect(), current_visible_rect_);
-
   // Explicitly check if the tile is outside the viewport. If so, we need to
   // return false, since occlusion for this tile is unknown.
-  // TODO(vmpstr): Since the current visible rect is really a viewport in
-  // layer space, we should probably clip tile query rect to tiling bounds
-  // or live tiles rect.
   if (tile_query_rect.IsEmpty())
     return false;
 
   if (contents_scale_ != 1.f) {
     tile_query_rect =
-        gfx::ScaleToEnclosingRect(tile_query_rect, 1.0f / contents_scale_);
+        gfx::ScaleToEnclosingRect(tile_query_rect, 1.f / contents_scale_);
   }
-
   return current_occlusion_in_layer_space_.IsOccluded(tile_query_rect);
 }
 
-bool PictureLayerTiling::IsTileRequiredForActivationIfVisible(
-    const Tile* tile) const {
-  DCHECK_EQ(PENDING_TREE, client_->GetTree());
+bool PictureLayerTiling::IsTileRequiredForActivation(const Tile* tile) const {
+  if (client_->GetTree() == PENDING_TREE) {
+    if (!can_require_tiles_for_activation_)
+      return false;
 
-  // This function assumes that the tile is visible (i.e. in the viewport).  The
-  // caller needs to make sure that this condition is met to ensure we don't
-  // block activation on tiles outside of the viewport.
+    if (resolution_ != HIGH_RESOLUTION)
+      return false;
 
-  // If we are not allowed to mark tiles as required for activation, then don't
-  // do it.
-  if (!can_require_tiles_for_activation_)
-    return false;
+    if (IsTileOccluded(tile))
+      return false;
 
-  if (resolution_ != HIGH_RESOLUTION)
-    return false;
+    bool tile_is_visible =
+        tile->content_rect().Intersects(current_visible_rect_);
+    if (!tile_is_visible)
+      return false;
 
-  if (IsTileOccluded(tile))
-    return false;
+    if (client_->RequiresHighResToDraw())
+      return true;
 
-  if (client_->RequiresHighResToDraw())
-    return true;
+    const PictureLayerTiling* active_twin =
+        client_->GetPendingOrActiveTwinTiling(this);
+    if (!active_twin || !TilingMatchesTileIndices(active_twin))
+      return true;
 
-  const PictureLayerTiling* twin_tiling =
-      client_->GetPendingOrActiveTwinTiling(this);
-  if (!twin_tiling)
-    return true;
+    if (active_twin->raster_source()->GetSize() != raster_source()->GetSize())
+      return true;
 
-  if (twin_tiling->raster_source()->GetSize() != raster_source()->GetSize())
-    return true;
+    if (active_twin->current_visible_rect_ != current_visible_rect_)
+      return true;
 
-  if (twin_tiling->current_visible_rect_ != current_visible_rect_)
+    Tile* twin_tile =
+        active_twin->TileAt(tile->tiling_i_index(), tile->tiling_j_index());
+    if (!twin_tile)
+      return false;
     return true;
+  }
 
-  Tile* twin_tile =
-      twin_tiling->TileAt(tile->tiling_i_index(), tile->tiling_j_index());
-  // If twin tile is missing, it might not have a recording, so we don't need
-  // this tile to be required for activation.
-  if (!twin_tile)
+  DCHECK(client_->GetTree() == ACTIVE_TREE);
+  const PictureLayerTiling* pending_twin =
+      client_->GetPendingOrActiveTwinTiling(this);
+  // If we don't have a pending tree, or the pending tree will overwrite the
+  // given tile, then it is not required for activation.
+  if (!pending_twin || !TilingMatchesTileIndices(pending_twin) ||
+      pending_twin->TileAt(tile->tiling_i_index(), tile->tiling_j_index())) {
     return false;
-
-  return true;
+  }
+  // Otherwise, ask the pending twin if this tile is required for activation.
+  return pending_twin->IsTileRequiredForActivation(tile);
 }
 
-bool PictureLayerTiling::IsTileRequiredForDrawIfVisible(
-    const Tile* tile) const {
-  DCHECK_EQ(ACTIVE_TREE, client_->GetTree());
-
-  // This function assumes that the tile is visible (i.e. in the viewport).
+bool PictureLayerTiling::IsTileRequiredForDraw(const Tile* tile) const {
+  if (client_->GetTree() == PENDING_TREE)
+    return false;
 
   if (resolution_ != HIGH_RESOLUTION)
     return false;
 
-  if (IsTileOccluded(tile))
+  bool tile_is_visible = current_visible_rect_.Intersects(tile->content_rect());
+  if (!tile_is_visible)
     return false;
 
+  if (IsTileOccludedOnCurrentTree(tile))
+    return false;
   return true;
 }
 
 void PictureLayerTiling::UpdateTileAndTwinPriority(Tile* tile) const {
-  WhichTree tree = client_->GetTree();
-  WhichTree twin_tree = tree == ACTIVE_TREE ? PENDING_TREE : ACTIVE_TREE;
-
-  tile->SetPriority(tree, ComputePriorityForTile(tile));
-  UpdateRequiredStateForTile(tile, tree);
-
-  const PictureLayerTiling* twin_tiling =
-      client_->GetPendingOrActiveTwinTiling(this);
-  if (!tile->is_shared() || !twin_tiling) {
-    tile->SetPriority(twin_tree, TilePriority());
-    tile->set_is_occluded(twin_tree, false);
-    if (twin_tree == PENDING_TREE)
-      tile->set_required_for_activation(false);
-    else
-      tile->set_required_for_draw(false);
-    return;
-  }
-
-  tile->SetPriority(twin_tree, twin_tiling->ComputePriorityForTile(tile));
-  twin_tiling->UpdateRequiredStateForTile(tile, twin_tree);
-}
-
-void PictureLayerTiling::UpdateRequiredStateForTile(Tile* tile,
-                                                    WhichTree tree) const {
-  if (tile->priority(tree).priority_bin == TilePriority::NOW) {
-    if (tree == PENDING_TREE) {
-      tile->set_required_for_activation(
-          IsTileRequiredForActivationIfVisible(tile));
-    } else {
-      tile->set_required_for_draw(IsTileRequiredForDrawIfVisible(tile));
-    }
-    tile->set_is_occluded(tree, IsTileOccluded(tile));
-    return;
-  }
-
-  // Non-NOW bin tiles are not required or occluded.
-  if (tree == PENDING_TREE)
-    tile->set_required_for_activation(false);
-  else
-    tile->set_required_for_draw(false);
-  tile->set_is_occluded(tree, false);
+  tile->set_priority(ComputePriorityForTile(tile));
+  tile->set_is_occluded(IsTileOccluded(tile));
+  tile->set_required_for_activation(IsTileRequiredForActivation(tile));
+  tile->set_required_for_draw(IsTileRequiredForDraw(tile));
 }
 
 void PictureLayerTiling::VerifyAllTilesHaveCurrentRasterSource() const {
@@ -874,6 +835,11 @@ TilePriority PictureLayerTiling::ComputePriorityForTile(
     return TilePriority(resolution_, TilePriority::NOW, 0);
   }
 
+  if (max_tile_priority_bin <= TilePriority::SOON &&
+      pending_visible_rect().Intersects(tile_bounds)) {
+    return TilePriority(resolution_, TilePriority::SOON, 0);
+  }
+
   DCHECK_GT(current_content_to_screen_scale_, 0.f);
   float distance_to_visible =
       current_visible_rect_.ManhattanInternalDistance(tile_bounds) *
@@ -891,20 +857,11 @@ TilePriority PictureLayerTiling::ComputePriorityForTile(
 
 void PictureLayerTiling::GetAllTilesAndPrioritiesForTracing(
     std::map<const Tile*, TilePriority>* tile_map) const {
-  const PictureLayerTiling* twin_tiling =
-      client_->GetPendingOrActiveTwinTiling(this);
   for (const auto& tile_pair : tiles_) {
     const Tile* tile = tile_pair.second.get();
     const TilePriority& priority = ComputePriorityForTile(tile);
-    // If the tile is shared, it means the twin also has the same tile.
-    // Otherwise, use the default priority.
-    const TilePriority& twin_priority =
-        (twin_tiling && tile->is_shared())
-            ? twin_tiling->ComputePriorityForTile(tile)
-            : TilePriority();
-
     // Store combined priority.
-    (*tile_map)[tile] = TilePriority(priority, twin_priority);
+    (*tile_map)[tile] = priority;
   }
 }