cc: Move LayerEvictionTileIterator to a separate file and make it a queue

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index 0af0d94f671a83744c1584966255b677fcf069e2..bf24b0ce8dc1b64395587327b659cba8f940fb2b 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -98,6 +98,14 @@ PictureLayerImpl::~PictureLayerImpl() {
   layer_tree_impl()->UnregisterPictureLayerImpl(this);
 }
 
+scoped_ptr<TilingSetEvictionQueue> PictureLayerImpl::CreateEvictionQueue(
+    TreePriority tree_priority) {
+  if (!tilings_)
+    return nullptr;

[vmpstr, 2014/11/21 18:08:23]

I think this should return some sort of a "default empty queue" instead of null,
that way the calling code will always get an object.

[USE eero AT chromium.org, 2014/11/25 11:42:42]

The only calling code (apart from perf/unit tests) is
cc::EvictionTilePriorityQueue::PairedTilingSetQueue which have to deal with
nulls anyway as it does not create "default empty queues" for non-existing
active or pending twin layers anyway. So in this particular case, IMO, "default
empty queues" would not simplify anything.

If you disagree, I can change this.

[vmpstr, 2014/11/25 17:37:04]

It simplifies the interface. When we call layer->CreateEvictionQueue(...); it
should return a queue. Typically, if we request something be created and it
returns a nullptr, it means that it wasn't possible to create it for whatever
reason (out of memory). 

In this case, that means if the queue that would be created is going to be
empty, we should still create it as an empty (default) queue. 

[USE eero AT chromium.org, 2014/11/26 09:17:19]

Acknowledged.

+  return make_scoped_ptr(
+      new TilingSetEvictionQueue(tilings_.get(), tree_priority));
+}
+
 const char* PictureLayerImpl::LayerTypeAsString() const {
   return "cc::PictureLayerImpl";
 }
@@ -1474,158 +1482,4 @@ void PictureLayerImpl::LayerRasterTileIterator::AdvanceToNextStage() {
   }
 }
 
-PictureLayerImpl::LayerEvictionTileIterator::LayerEvictionTileIterator()
-    : layer_(nullptr),
-      tree_priority_(SAME_PRIORITY_FOR_BOTH_TREES),
-      current_category_(PictureLayerTiling::EVENTUALLY),
-      current_tiling_range_type_(PictureLayerTilingSet::HIGHER_THAN_HIGH_RES),
-      current_tiling_(0u) {
-}
-
-PictureLayerImpl::LayerEvictionTileIterator::LayerEvictionTileIterator(
-    PictureLayerImpl* layer,
-    TreePriority tree_priority)
-    : layer_(layer),
-      tree_priority_(tree_priority),
-      current_category_(PictureLayerTiling::EVENTUALLY),
-      current_tiling_range_type_(PictureLayerTilingSet::HIGHER_THAN_HIGH_RES),
-      current_tiling_(0u) {
-  // Early out if the layer has no tilings.
-  if (!layer_->tilings_ || !layer_->tilings_->num_tilings())
-    return;
-
-  current_tiling_ = CurrentTilingRange().start - 1u;
-  do {
-    if (!AdvanceToNextTiling())
-      break;
-
-    current_iterator_ = PictureLayerTiling::TilingEvictionTileIterator(
-        layer_->tilings_->tiling_at(CurrentTilingIndex()),
-        tree_priority,
-        current_category_);
-  } while (!current_iterator_);
-}
-
-PictureLayerImpl::LayerEvictionTileIterator::~LayerEvictionTileIterator() {
-}
-
-Tile* PictureLayerImpl::LayerEvictionTileIterator::operator*() {
-  DCHECK(*this);
-  return *current_iterator_;
-}
-
-const Tile* PictureLayerImpl::LayerEvictionTileIterator::operator*() const {
-  DCHECK(*this);
-  return *current_iterator_;
-}
-
-PictureLayerImpl::LayerEvictionTileIterator&
-PictureLayerImpl::LayerEvictionTileIterator::
-operator++() {
-  DCHECK(*this);
-  ++current_iterator_;
-  while (!current_iterator_) {
-    if (!AdvanceToNextTiling())
-      break;
-
-    current_iterator_ = PictureLayerTiling::TilingEvictionTileIterator(
-        layer_->tilings_->tiling_at(CurrentTilingIndex()),
-        tree_priority_,
-        current_category_);
-  }
-  return *this;
-}
-
-PictureLayerImpl::LayerEvictionTileIterator::operator bool() const {
-  return !!current_iterator_;
-}
-
-bool PictureLayerImpl::LayerEvictionTileIterator::AdvanceToNextCategory() {
-  switch (current_category_) {
-    case PictureLayerTiling::EVENTUALLY:
-      current_category_ =
-          PictureLayerTiling::EVENTUALLY_AND_REQUIRED_FOR_ACTIVATION;
-      return true;
-    case PictureLayerTiling::EVENTUALLY_AND_REQUIRED_FOR_ACTIVATION:
-      current_category_ = PictureLayerTiling::SOON;
-      return true;
-    case PictureLayerTiling::SOON:
-      current_category_ = PictureLayerTiling::SOON_AND_REQUIRED_FOR_ACTIVATION;
-      return true;
-    case PictureLayerTiling::SOON_AND_REQUIRED_FOR_ACTIVATION:
-      current_category_ = PictureLayerTiling::NOW;
-      return true;
-    case PictureLayerTiling::NOW:
-      current_category_ = PictureLayerTiling::NOW_AND_REQUIRED_FOR_ACTIVATION;
-      return true;
-    case PictureLayerTiling::NOW_AND_REQUIRED_FOR_ACTIVATION:
-      return false;
-  }
-  NOTREACHED();
-  return false;
-}
-
-bool
-PictureLayerImpl::LayerEvictionTileIterator::AdvanceToNextTilingRangeType() {
-  switch (current_tiling_range_type_) {
-    case PictureLayerTilingSet::HIGHER_THAN_HIGH_RES:
-      current_tiling_range_type_ = PictureLayerTilingSet::LOWER_THAN_LOW_RES;
-      return true;
-    case PictureLayerTilingSet::LOWER_THAN_LOW_RES:
-      current_tiling_range_type_ =
-          PictureLayerTilingSet::BETWEEN_HIGH_AND_LOW_RES;
-      return true;
-    case PictureLayerTilingSet::BETWEEN_HIGH_AND_LOW_RES:
-      current_tiling_range_type_ = PictureLayerTilingSet::LOW_RES;
-      return true;
-    case PictureLayerTilingSet::LOW_RES:
-      current_tiling_range_type_ = PictureLayerTilingSet::HIGH_RES;
-      return true;
-    case PictureLayerTilingSet::HIGH_RES:
-      if (!AdvanceToNextCategory())
-        return false;
-
-      current_tiling_range_type_ = PictureLayerTilingSet::HIGHER_THAN_HIGH_RES;
-      return true;
-  }
-  NOTREACHED();
-  return false;
-}
-
-bool PictureLayerImpl::LayerEvictionTileIterator::AdvanceToNextTiling() {
-  DCHECK_NE(current_tiling_, CurrentTilingRange().end);
-  ++current_tiling_;
-  while (current_tiling_ == CurrentTilingRange().end) {
-    if (!AdvanceToNextTilingRangeType())
-      return false;
-
-    current_tiling_ = CurrentTilingRange().start;
-  }
-  return true;
-}
-
-PictureLayerTilingSet::TilingRange
-PictureLayerImpl::LayerEvictionTileIterator::CurrentTilingRange() const {
-  return layer_->tilings_->GetTilingRange(current_tiling_range_type_);
-}
-
-size_t PictureLayerImpl::LayerEvictionTileIterator::CurrentTilingIndex() const {
-  DCHECK_NE(current_tiling_, CurrentTilingRange().end);
-  switch (current_tiling_range_type_) {
-    case PictureLayerTilingSet::HIGHER_THAN_HIGH_RES:
-    case PictureLayerTilingSet::LOW_RES:
-    case PictureLayerTilingSet::HIGH_RES:
-      return current_tiling_;
-    // Tilings in the following ranges are accessed in reverse order.
-    case PictureLayerTilingSet::BETWEEN_HIGH_AND_LOW_RES:
-    case PictureLayerTilingSet::LOWER_THAN_LOW_RES: {
-      PictureLayerTilingSet::TilingRange tiling_range = CurrentTilingRange();
-      size_t current_tiling_range_offset = current_tiling_ - tiling_range.start;
-      return tiling_range.end - 1 - current_tiling_range_offset;
-    }
-  }
-  NOTREACHED();
-  return 0;
-}
-
 }  // namespace cc