Support attributionsrc on <area> (#1465)

index.bs

@@ -139,6 +139,7 @@ interface mixin HTMLAttributionSrcElementUtils {
 };
 
 HTMLAnchorElement includes HTMLAttributionSrcElementUtils;
+HTMLAreaElement includes HTMLAttributionSrcElementUtils;
 HTMLImageElement includes HTMLAttributionSrcElementUtils;
 HTMLScriptElement includes HTMLAttributionSrcElementUtils;
 </pre>
@@ -149,6 +150,10 @@ Add the following <a spec=html>content attributes</a>:
 :: <dfn for="a" element-attr>attributionsrc</dfn> - A [=string=] containing
     zero or more [=URLs=] to which a background attributionsrc request will be
     made when the <{a}> is navigated.
+: <{area}>
+:: <dfn for="area" element-attr>attributionsrc</dfn> - A [=string=] containing
+    zero or more [=URLs=] to which a background attributionsrc request will be
+    made when the <{area}> is navigated.
 : <{img}>
 :: <dfn for="img" element-attr>attributionsrc</dfn> - A [=string=] containing
     zero or more [=URLs=] to which a background attributionsrc request will be