Keep track of fixed positioning in accessibility tree.

third_party/WebKit/Source/modules/accessibility/AXObject.h

Index: third_party/WebKit/Source/modules/accessibility/AXObject.h
diff --git a/third_party/WebKit/Source/modules/accessibility/AXObject.h b/third_party/WebKit/Source/modules/accessibility/AXObject.h
index ba79e1eb85a8c64ee3511a0a174110eb08e6b51a..0f0c04cf498c284a57660067d30fa9c7294f7a65 100644
--- a/third_party/WebKit/Source/modules/accessibility/AXObject.h
+++ b/third_party/WebKit/Source/modules/accessibility/AXObject.h
@@ -683,9 +683,12 @@ class MODULES_EXPORT AXObject : public GarbageCollectedFinalized<AXObject> {
   // not null, walk up to its container and offset by the container's offset
   // from origin, the container's scroll position if any, and apply the
   // container's transform.  Do this until you reach the root of the tree.
+  // If |out_is_fixed_positioned| is set, the scroll position of the container
+  // should be ignored.
   virtual void GetRelativeBounds(AXObject** out_container,
                                  FloatRect& out_bounds_in_container,
-                                 SkMatrix44& out_container_transform) const;
+                                 SkMatrix44& out_container_transform,
+                                 bool& out_is_fixed_positioned) const;
 
   // Get the bounds in frame-relative coordinates as a LayoutRect.
   LayoutRect GetBoundsInFrameCoordinates() const;
@@ -853,6 +856,15 @@ class MODULES_EXPORT AXObject : public GarbageCollectedFinalized<AXObject> {
     return nullptr;
   }
 
+  // A simpler variant of GetRelativeBounds that can be overridden by
+  // subclasses that don't need to handle transformations or fixed
+  // positionining. Returns true if overridden by this subclass.
+  virtual bool GetSimpleRelativeBounds(
+      AXObject** out_container,
+      FloatRect& out_bounds_in_container) const {
+    return false;
+  }
+
   const AXObject* InertRoot() const;
 
   mutable Member<AXObject> parent_;