cc: Clean up iterator template to only take 1 parameter.

cc/layers/layer_iterator.h

Index: cc/layers/layer_iterator.h
diff --git a/cc/layers/layer_iterator.h b/cc/layers/layer_iterator.h
index 5b13273254574107c0fccb23d8b327f5729653e0..1e12ee43a18758b8b5fa524f49d882983aeb80f3 100644
--- a/cc/layers/layer_iterator.h
+++ b/cc/layers/layer_iterator.h
@@ -5,7 +5,6 @@
 #ifndef CC_LAYERS_LAYER_ITERATOR_H_
 #define CC_LAYERS_LAYER_ITERATOR_H_
 
-#include "base/memory/ref_counted.h"
 #include "cc/base/cc_export.h"
 #include "cc/trees/layer_tree_host_common.h"
 
@@ -19,11 +18,7 @@ namespace cc {
 //
 // void DoStuffOnLayers(
 //     const RenderSurfaceLayerList& render_surface_layer_list) {
-//   typedef LayerIterator<Layer,
-//                         RenderSurfaceLayerList,
-//                         RenderSurface,
-//                         LayerIteratorActions::FrontToBack>
-//       LayerIteratorType;
+//   typedef LayerIterator<Layer> LayerIteratorType;
 //
 //   LayerIteratorType end =
 //       LayerIteratorType::End(&render_surface_layer_list);
@@ -103,17 +98,20 @@ template <typename LayerType> struct LayerIteratorPosition {
   LayerType* current_layer;
 };
 
+struct LayerIteratorPadding {
+  // This struct has nothing in it! It exists to make the LayerIterator a bit
+  // larger for debugging some weird behaviour when this CL previously landed.
+  // See crbug.com/345757 for more details.
+  void Foo() {}
+};
+
 // An iterator class for walking over layers in the
 // RenderSurface-Layer tree.
-template <typename LayerType,
-          typename LayerList,
-          typename RenderSurfaceType,
-          typename IteratorActionType>
+template <typename LayerType>
 class LayerIterator {
-  typedef LayerIterator<LayerType,
-                        LayerList,
-                        RenderSurfaceType,
-                        IteratorActionType> LayerIteratorType;
+  typedef LayerIterator<LayerType> LayerIteratorType;
+  typedef typename LayerType::RenderSurfaceListType LayerList;
+  typedef typename LayerType::RenderSurfaceType RenderSurfaceType;
 
  public:
   LayerIterator() : render_surface_layer_list_(NULL) {}
@@ -126,7 +124,7 @@ class LayerIterator {
   }
 
   LayerIteratorType& operator++() {
-    actions_.Next(this);
+    MoveToNext();
     return *this;
   }
   bool operator==(const LayerIterator& other) const {
@@ -176,15 +174,81 @@ class LayerIterator {
     for (size_t i = 0; i < render_surface_layer_list->size(); ++i) {
       if (!render_surface_layer_list->at(i)->render_surface()) {
         NOTREACHED();
-        actions_.End(this);
+        MoveToEnd();
         return;
       }
     }
 
     if (start && !render_surface_layer_list->empty())
-      actions_.Begin(this);
+      MoveToBegin();
     else
-      actions_.End(this);
+      MoveToEnd();
+  }
+
+  void MoveToBegin() {
+    target_render_surface_layer_index_ = 0;
+    current_layer_index_ = target_render_surface_children().size() - 1;
+    MoveToHighestInSubtree();
+  }
+
+  void MoveToEnd() {
+    target_render_surface_layer_index_ =
+        LayerIteratorValue::kInvalidTargetRenderSurfaceLayerIndex;
+    current_layer_index_ = 0;
+  }
+
+  void MoveToNext() {
+    // Moves to the previous layer in the current RS layer list.
+    // Then we check if the new current layer has its own RS,
+    // in which case there are things in that RS layer list that are higher,
+    // so we find the highest layer in that subtree.
+    // If we move back past the front of the list,
+    // we jump up to the previous RS layer list, picking up again where we
+    // had previously recursed into the current RS layer list.
+
+    if (!current_layer_represents_target_render_surface()) {
+      // Subtracting one here will eventually cause the current layer
+      // to become that layer representing the target render surface.
+      --current_layer_index_;
+      MoveToHighestInSubtree();
+    } else {
+      while (current_layer_represents_target_render_surface()) {
+        if (!target_render_surface_layer_index_) {
+          // End of the list.
+          target_render_surface_layer_index_ =
+              LayerIteratorValue::kInvalidTargetRenderSurfaceLayerIndex;
+          current_layer_index_ = 0;
+          return;
+        }
+        target_render_surface_layer_index_ =
+            target_render_surface()->target_render_surface_layer_index_history_;
+        current_layer_index_ =
+            target_render_surface()->current_layer_index_history_;
+      }
+    }
+  }
+
+  void MoveToHighestInSubtree() {
+    if (current_layer_represents_target_render_surface())
+      return;
+    while (current_layer_represents_contributing_render_surface()) {
+      // Save where we were in the current target surface, move to the next one,
+      // and save the target surface that we came from there
+      // so we can go back to it.
+      target_render_surface()->current_layer_index_history_ =
+          current_layer_index_;
+      int previous_target_render_surface_layer =
+          target_render_surface_layer_index_;
+
+      for (LayerType* layer = current_layer();
+           target_render_surface_layer() != layer;
+           ++target_render_surface_layer_index_) {
+      }
+      current_layer_index_ = target_render_surface_children().size() - 1;
+
+      target_render_surface()->target_render_surface_layer_index_history_ =
+          previous_target_render_surface_layer;
+    }
   }
 
   inline LayerType* current_layer() const {
@@ -209,7 +273,7 @@ class LayerIterator {
     return target_render_surface()->layer_list();
   }
 
-  IteratorActionType actions_;
+  LayerIteratorPadding padding_;
   const LayerList* render_surface_layer_list_;
 
   // The iterator's current position.
@@ -228,44 +292,6 @@ class LayerIterator {
   // the target surface, this is done by setting the current_layerIndex
   // to a value of LayerIteratorValue::LayerRepresentingTargetRenderSurface.
   int current_layer_index_;
-
-  friend struct LayerIteratorActions;
-};
-
-// Orderings for iterating over the RenderSurface-Layer tree.
-struct CC_EXPORT LayerIteratorActions {
-  // Walks layers sorted by z-order from front to back
-  class CC_EXPORT FrontToBack {
-   public:
-    template <typename LayerType,
-              typename LayerList,
-              typename RenderSurfaceType,
-              typename ActionType>
-    void Begin(
-        LayerIterator<LayerType, LayerList, RenderSurfaceType, ActionType>* it);
-
-    template <typename LayerType,
-              typename LayerList,
-              typename RenderSurfaceType,
-              typename ActionType>
-    void End(
-        LayerIterator<LayerType, LayerList, RenderSurfaceType, ActionType>* it);
-
-    template <typename LayerType,
-              typename LayerList,
-              typename RenderSurfaceType,
-              typename ActionType>
-    void Next(
-        LayerIterator<LayerType, LayerList, RenderSurfaceType, ActionType>* it);
-
-   private:
-    template <typename LayerType,
-              typename LayerList,
-              typename RenderSurfaceType,
-              typename ActionType>
-    void GoToHighestInSubtree(
-        LayerIterator<LayerType, LayerList, RenderSurfaceType, ActionType>* it);
-  };
 };
 
 }  // namespace cc