add SecureContext and allowed to use check

index.html

@@ -103,7 +103,7 @@ 
         
         
           partial interface Navigator {
-            boolean canShare(optional ShareData data = {});
+            [SecureContext] boolean canShare(optional ShareData data = {});
             [SecureContext] Promise<undefined> share(optional ShareData data = {});
           };
         
@@ -146,6 +146,10 @@ 
             |data:ShareData|, run the following steps:
           
           
+            If the current settings object's responsible document is not
+            allowed to use the "[=web-share-feature|web-share=]"
+            permission, return false.
+            
             Let |base| be [=this=]'s [=relevant settings object=]'s
             [=environment settings object/API base URL=].