Add localToAbsoluteTransform and localToAncestorTransform.

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

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index 8614a89b100a0d259dabca599e1958db3b90da9f..85850a5ba74da1f3dcdd356cff3bfd803b389cda 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -987,10 +987,25 @@ public:
     }
 
     // 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);