Add sparse accessibility attribute interface to Blink

third_party/WebKit/public/web/WebAXEnums.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
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   WebAXDescriptionFromContents,
   WebAXDescriptionFromRelatedElement,
 };
 
 // Text affinity for the start or end of a selection.
 enum WebAXTextAffinity {
   WebAXTextAffinityUpstream,
   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