Add localToAbsoluteTransform and localToAncestorTransform.

third_party/WebKit/Source/core/layout/LayoutObject.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 969 matching lines @@
     // Otherwise:
     //   If TraverseDocumentBoundaries is specified, the input quad is in the space of the local root frame.
     //   Otherwise, the input quad is in the space of the containing frame.
     FloatQuad ancestorToLocalQuad(LayoutBoxModelObject*, const FloatQuad&, MapCoordinatesFlags mode = 0) const;
     FloatQuad absoluteToLocalQuad(const FloatQuad& quad, MapCoordinatesFlags mode = 0) const
     {
         return ancestorToLocalQuad(nullptr, quad, mode);
     }
 
     // Convert a local quad into the coordinate system of container, taking transforms into account.
+    // If the LayoutBoxModelObject ancestor is non-null, the result will be in the space of the ancestor.
+    // Otherwise:
+    //   If TraverseDocumentBoundaries is specified, the result will be in the space of the local root frame.
+    //   Otherwise, the result will be in the space of the containing frame.
     FloatQuad localToAncestorQuad(const FloatQuad&, const LayoutBoxModelObject* ancestor, MapCoordinatesFlags = 0, bool* wasFixed = nullptr) const;
     FloatPoint localToAncestorPoint(const FloatPoint&, const LayoutBoxModelObject* ancestor, MapCoordinatesFlags = 0, bool* wasFixed = nullptr, const PaintInvalidationState* = nullptr) const;
     void localToAncestorRects(Vector<LayoutRect>&, const LayoutBoxModelObject* ancestor, const LayoutPoint& preOffset, const LayoutPoint& postOffset) const;
 
+    // Return the transformation matrix to map points from local to the coordinate system of a container, taking transforms into account.
+    // If the LayoutBoxModelObject ancestor is non-null, the result will transform into the space of the ancestor.

[chrishtr, 2016/03/15 23:06:42]

You can just refer to the comments for localToAncestorQuad for behavior w.r.t.
the
|ancestor| parameter, rather than copying the comment.

[dmazzoni, 2016/03/16 05:42:01]

Done.

+    // Otherwise:
+    //   If TraverseDocumentBoundaries is specified, the result will transform into the space of the local root frame.
+    //   Otherwise, the result will transform into the space of the containing frame.
+    TransformationMatrix localToAncestorTransform(const LayoutBoxModelObject* ancestor, MapCoordinatesFlags = 0, bool* wasFixed = nullptr) const;
+    TransformationMatrix localToAbsoluteTransform(MapCoordinatesFlags mode = 0, bool* wasFixed = nullptr) const
+    {
+        return localToAncestorTransform(nullptr, mode, wasFixed);
+    }
+
     // Convert a local point into the coordinate system of backing coordinates. Also returns the backing layer if needed.
     FloatPoint localToInvalidationBackingPoint(const LayoutPoint&, PaintLayer** backingLayer = nullptr);
 
     // Return the offset from the container() layoutObject (excluding transforms). In multi-column layout,
     // different offsets apply at different points, so return the offset that applies to the given point.
     virtual LayoutSize offsetFromContainer(const LayoutObject*, const LayoutPoint&, bool* offsetDependsOnPoint = nullptr) const;
     // Return the offset from an object up the container() chain. Asserts that none of the intermediate objects have transforms.
     LayoutSize offsetFromAncestorContainer(const LayoutObject*) const;
 
     virtual void absoluteRects(Vector<IntRect>&, const LayoutPoint&) const { }
@@ skipping 1151 matching lines @@
 void showTree(const blink::LayoutObject*);
 void showLineTree(const blink::LayoutObject*);
 void showLayoutTree(const blink::LayoutObject* object1);
 // We don't make object2 an optional parameter so that showLayoutTree
 // can be called from gdb easily.
 void showLayoutTree(const blink::LayoutObject* object1, const blink::LayoutObject* object2);
 
 #endif
 
 #endif // LayoutObject_h