Implement merging non-composited paint property nodes in the PACompositor.

third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h

Index: third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h b/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
index c59fc27f16496f21a0052eded86c7f093ef9d3da..19555592996153b78883df9520f1af9cc9f6b1c2 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
@@ -18,7 +18,7 @@ namespace blink {
 // other objects.  RefPtrs are used to guard against use-after-free bugs and
 // DCHECKs ensure PropertyTreeState never retains the last reference to a
 // property tree node.
-class PropertyTreeState {
+class PLATFORM_EXPORT PropertyTreeState {
  public:
   PropertyTreeState(const TransformPaintPropertyNode* transform,
                     const ClipPaintPropertyNode* clip,
@@ -34,6 +34,8 @@ class PropertyTreeState {
     DCHECK(!m_scroll || !m_scroll->hasOneRef());
   }
 
+  bool hasDirectCompositingReasons() const;
+
   const TransformPaintPropertyNode* transform() const {
     DCHECK(!m_transform || !m_transform->hasOneRef());
     return m_transform.get();
@@ -66,6 +68,50 @@ class PropertyTreeState {
     m_scroll = std::move(node);
   }
 
+  enum InnermostNode {
+    None,  // None means that all nodes are their root values
+    Transform,
+    Clip,
+    Effect,
+  };
+
+  // There is always a well-defined order in which the transform, clip
+  // and effects of a PropertyTreeState apply. This method returns which
+  // of them applies first to content drawn with this PropertyTreeState.
+  // Note that it may be the case that multiple nodes from the same tree apply
+  // before any from another tree. This can happen, for example, if multiple
+  // effects or clips apply to a descendant transform state from the transform
+  // node.
+  //
+  // This method is meant to be used in concert with
+  // |PropertyTreeStateIterator|, which allows one to iterate over the nodes in
+  // the order in which they apply.
+  //
+  // Example:
+  //
+  //  Transform tree      Clip tree      Effect tree
+  //  ~~~~~~~~~~~~~~      ~~~~~~~~~      ~~~~~~~~~~~
+  //       Root              Root            Root
+  //        |                 |               |
+  //        T                 C               E
+  //
+  // Suppose that PropertyTreeState(T, C, E).innerMostNode() is E, and
+  // PropertytreeState(T, C, Root).innermostNode() is C. Then a PaintChunk
+  // that has propertyTreeState = PropertyTreeState(T, C, E) can be painted
+  // with the following display list structure:
+  //
+  // [BeginTransform] [BeginClip] [BeginEffect] PaintChunk drawings
+  //    [EndEffect] [EndClip] [EndTransform]
+  //
+  // The PropertyTreeStateIterator will behave like this:
+  //
+  // PropertyTreeStateIterator iterator(PropertyTreeState(T, C, E));
+  // DCHECK(iterator.innermostNode() == Effect);
+  // DCHECK(iterator.next()->innermostNode() == Clip);
+  // DCHECK(iterator.next()->innermostNode() == Transform);
+  // DCHECK(iterator.next()->innermostNode() == None);
+  InnermostNode innermostNode() const;
+
  private:
   RefPtr<const TransformPaintPropertyNode> m_transform;
   RefPtr<const ClipPaintPropertyNode> m_clip;
@@ -78,6 +124,21 @@ inline bool operator==(const PropertyTreeState& a, const PropertyTreeState& b) {
          a.effect() == b.effect() && a.scroll() == b.scroll();
 }
 
+// Iterates over the sequence transforms, clips and effects for a
+// PropertyTreeState between that state and the "root" state (all nodes equal
+// to *::Root()), in the order that they apply.
+//
+// See also PropertyTreeState::innermostNode for a more detailed example.
+class PLATFORM_EXPORT PropertyTreeStateIterator {
+ public:
+  PropertyTreeStateIterator(const PropertyTreeState& properties)
+      : m_properties(properties) {}
+  const PropertyTreeState* next();
+
+ private:
+  PropertyTreeState m_properties;
+};
+
 }  // namespace blink
 
 #endif  // PropertyTreeState_h