Add sparse accessibility attribute interface to Blink

third_party/WebKit/public/web/WebAXEnums.h

Index: third_party/WebKit/public/web/WebAXEnums.h
diff --git a/third_party/WebKit/public/web/WebAXEnums.h b/third_party/WebKit/public/web/WebAXEnums.h
index 599dfd87a482021595c5a7ba59ca3683654705d1..1b72d74bcb7d25326747dab98c632377394d2852 100644
--- a/third_party/WebKit/public/web/WebAXEnums.h
+++ b/third_party/WebKit/public/web/WebAXEnums.h
@@ -340,6 +340,44 @@ enum WebAXTextAffinity {
   WebAXTextAffinityDownstream
 };
 
+//
+// Sparse accessibility attributes
+//
+// The following enums represent accessibility attributes that apply
+// to only a small fraction of WebAXObjects. Rather than the client
+// asking each WebAXObject for the value of each accessibility
+// attribute, it can call a single function to query for all
+// sparse attributes at the same time. Any sparse attributes that
+// are present are returned via a callback consisting of an attribute
+// key enum and an attribute value.
+//
+
+// Sparse attributes of a WebAXObject whose value is either true or
+// false. In order for it to be a sparse attribute the default value
+// must be false.
+enum class WebAXBoolAttribute {};
+
+// Sparse attributes of a WebAXObject whose value is a string.
+// In order for it to be a sparse attribute the default value
+// must be "".
+enum class WebAXStringAttribute {};
+
+// Sparse attributes of a WebAXObject whose value is a reference to
+// another WebAXObject within the same frame. In order for it to be a
+// sparse attribute the default value must be the null WebAXObject.
+enum class WebAXObjectAttribute {
+  AriaActiveDescendant,
+};
+
+// Sparse attributes of a WebAXObject whose value is a vector of
+// references to other WebAXObjects within the same frame. In order
+// for it to be a sparse attribute the default value must be the
+// empty vector.
+enum class WebAXObjectVectorAttribute {
+  AriaControls,
+  AriaFlowTo,
+};
+
 }  // namespace blink
 
 #endif