Normalize types of values returned by locators (#626)

Consistently return a WebDriver "error" type or a WebDriver "success"
type to support invocation of these algorithms using WebDriver's "try".

Author: jugglinmike

index.bs

@@ -2965,9 +2965,9 @@ To <dfn>locate nodes using CSS</dfn> with given |context target|, |context nodes
 
     1. If |maximum returned node count| is not null and [=list/size=] of
        |returned nodes| is equal to |maximum returned node count|,
-       return |returned nodes|.
+       return [=success=] with data |returned nodes|.
 
-1. Return |returned nodes|.
+1. Return [=success=] with data |returned nodes|.
 
 </div>
 
@@ -3006,11 +3006,11 @@ without going via the ECMAScript runtime.
 
       1. If |maximum returned node count| not null and [=list/size=] of
          |returned nodes| is equal to |maximum returned node count|,
-         return |returned nodes|.
+         return [=success=] with data |returned nodes|.
 
       1. Set |index| to |index| + 1.
 
-1. Return |returned nodes|.
+1. Return [=success=] with data |returned nodes|.
 
 </div>
 
@@ -3072,7 +3072,7 @@ and |session|:
    in |returned nodes| with an index greater than or equal to |maximum returned
    node count|.
 
-1. Return |returned nodes|.
+1. Return [=success=] with data |returned nodes|.
 
 </div>