Make scroll translation transform nodes reference scroll nodes

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

Index: third_party/WebKit/Source/platform/graphics/paint/ScrollPaintPropertyNode.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/ScrollPaintPropertyNode.h b/third_party/WebKit/Source/platform/graphics/paint/ScrollPaintPropertyNode.h
index df6307e746d45a939c1569fad94e9b2ccbe3e264..8ed94971059f9ae4f66bdbdb5a472eca732694fe 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/ScrollPaintPropertyNode.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/ScrollPaintPropertyNode.h
@@ -7,8 +7,6 @@
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatSize.h"
-#include "platform/graphics/CompositorElementId.h"
-#include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "platform/scroll/MainThreadScrollingReason.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
@@ -21,9 +19,10 @@ namespace blink {
 
 using MainThreadScrollingReasons = uint32_t;
 
-// A scroll node contains auxiliary scrolling information for threaded scrolling
-// which includes how far an area can be scrolled, which transform node contains
-// the scroll offset, etc.
+// A scroll node contains auxiliary scrolling information which includes how far
+// an area can be scrolled, main thread scrolling reasons, etc. Scroll nodes
+// are owned by TransformPaintPropertyNodes that are used for the scroll offset
+// translation.

[pdr., 2017/01/25 19:51:09]

Walter pointed out that we should put a comment here noting that the scroll
paint property tree differs from the other trees since it is (or will be)
embedded in the transform tree. We could even consider naming this
RareScrollNode or something like that.

 //
 // Main thread scrolling reasons force scroll updates to go to the main thread
 // and can have dependencies on other nodes. For example, all parents of a
@@ -36,49 +35,35 @@ class PLATFORM_EXPORT ScrollPaintPropertyNode
 
   static PassRefPtr<ScrollPaintPropertyNode> create(
       PassRefPtr<const ScrollPaintPropertyNode> parent,
-      PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
       const IntSize& clip,
       const IntSize& bounds,
       bool userScrollableHorizontal,
       bool userScrollableVertical,
-      MainThreadScrollingReasons mainThreadScrollingReasons,
-      const CompositorElementId& compositorElementId = CompositorElementId()) {
+      MainThreadScrollingReasons mainThreadScrollingReasons) {
     return adoptRef(new ScrollPaintPropertyNode(
-        std::move(parent), std::move(scrollOffsetTranslation), clip, bounds,
-        userScrollableHorizontal, userScrollableVertical,
-        mainThreadScrollingReasons, compositorElementId));
+        std::move(parent), clip, bounds, userScrollableHorizontal,
+        userScrollableVertical, mainThreadScrollingReasons));
   }
 
-  void update(
-      PassRefPtr<const ScrollPaintPropertyNode> parent,
-      PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
-      const IntSize& clip,
-      const IntSize& bounds,
-      bool userScrollableHorizontal,
-      bool userScrollableVertical,
-      MainThreadScrollingReasons mainThreadScrollingReasons,
-      CompositorElementId compositorElementId = CompositorElementId()) {
+  void update(PassRefPtr<const ScrollPaintPropertyNode> parent,
+              const IntSize& clip,
+              const IntSize& bounds,
+              bool userScrollableHorizontal,
+              bool userScrollableVertical,
+              MainThreadScrollingReasons mainThreadScrollingReasons) {
     DCHECK(!isRoot());
     DCHECK(parent != this);
     m_parent = parent;
-    DCHECK(scrollOffsetTranslation->matrix().isIdentityOr2DTranslation());
-    m_scrollOffsetTranslation = scrollOffsetTranslation;
     m_clip = clip;
     m_bounds = bounds;
     m_userScrollableHorizontal = userScrollableHorizontal;
     m_userScrollableVertical = userScrollableVertical;
     m_mainThreadScrollingReasons = mainThreadScrollingReasons;
-    m_compositorElementId = compositorElementId;
   }
 
   const ScrollPaintPropertyNode* parent() const { return m_parent.get(); }
   bool isRoot() const { return !m_parent; }
 
-  // Transform that the scroll is relative to.
-  const TransformPaintPropertyNode* scrollOffsetTranslation() const {
-    return m_scrollOffsetTranslation.get();
-  }
-
   // The clipped area that contains the scrolled content.
   const IntSize& clip() const { return m_clip; }
 
@@ -93,10 +78,6 @@ class PLATFORM_EXPORT ScrollPaintPropertyNode
     return m_mainThreadScrollingReasons;
   }
 
-  const CompositorElementId& compositorElementId() const {
-    return m_compositorElementId;
-  }
-
   // Main thread scrolling reason for the threaded scrolling disabled setting.
   bool threadedScrollingDisabled() const {
     return m_mainThreadScrollingReasons &
@@ -115,22 +96,19 @@ class PLATFORM_EXPORT ScrollPaintPropertyNode
   PassRefPtr<ScrollPaintPropertyNode> clone() const {
     RefPtr<ScrollPaintPropertyNode> cloned =
         adoptRef(new ScrollPaintPropertyNode(
-            m_parent, m_scrollOffsetTranslation, m_clip, m_bounds,
-            m_userScrollableHorizontal, m_userScrollableVertical,
-            m_mainThreadScrollingReasons, m_compositorElementId));
+            m_parent, m_clip, m_bounds, m_userScrollableHorizontal,
+            m_userScrollableVertical, m_mainThreadScrollingReasons));
     return cloned;
   }
 
   // The equality operator is used by FindPropertiesNeedingUpdate.h for checking
   // if a scroll node has changed.
   bool operator==(const ScrollPaintPropertyNode& o) const {
-    return m_parent == o.m_parent &&
-           m_scrollOffsetTranslation == o.m_scrollOffsetTranslation &&
-           m_clip == o.m_clip && m_bounds == o.m_bounds &&
+    return m_parent == o.m_parent && m_clip == o.m_clip &&
+           m_bounds == o.m_bounds &&
            m_userScrollableHorizontal == o.m_userScrollableHorizontal &&
            m_userScrollableVertical == o.m_userScrollableVertical &&
-           m_mainThreadScrollingReasons == o.m_mainThreadScrollingReasons &&
-           m_compositorElementId == o.m_compositorElementId;
+           m_mainThreadScrollingReasons == o.m_mainThreadScrollingReasons;
   }
 
   String toTreeString() const;
@@ -139,34 +117,25 @@ class PLATFORM_EXPORT ScrollPaintPropertyNode
   String toString() const;
 
  private:
-  ScrollPaintPropertyNode(
-      PassRefPtr<const ScrollPaintPropertyNode> parent,
-      PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
-      IntSize clip,
-      IntSize bounds,
-      bool userScrollableHorizontal,
-      bool userScrollableVertical,
-      MainThreadScrollingReasons mainThreadScrollingReasons,
-      CompositorElementId compositorElementId)
+  ScrollPaintPropertyNode(PassRefPtr<const ScrollPaintPropertyNode> parent,
+                          IntSize clip,
+                          IntSize bounds,
+                          bool userScrollableHorizontal,
+                          bool userScrollableVertical,
+                          MainThreadScrollingReasons mainThreadScrollingReasons)
       : m_parent(parent),
-        m_scrollOffsetTranslation(scrollOffsetTranslation),
         m_clip(clip),
         m_bounds(bounds),
         m_userScrollableHorizontal(userScrollableHorizontal),
         m_userScrollableVertical(userScrollableVertical),
-        m_mainThreadScrollingReasons(mainThreadScrollingReasons),
-        m_compositorElementId(compositorElementId) {
-    DCHECK(m_scrollOffsetTranslation->matrix().isIdentityOr2DTranslation());
-  }
+        m_mainThreadScrollingReasons(mainThreadScrollingReasons) {}
 
   RefPtr<const ScrollPaintPropertyNode> m_parent;
-  RefPtr<const TransformPaintPropertyNode> m_scrollOffsetTranslation;
   IntSize m_clip;
   IntSize m_bounds;
   bool m_userScrollableHorizontal : 1;
   bool m_userScrollableVertical : 1;
   MainThreadScrollingReasons m_mainThreadScrollingReasons;
-  CompositorElementId m_compositorElementId;
 };
 
 // Redeclared here to avoid ODR issues.