Add a convenience ok getter on Response (fixes #18)

Overview.html

@@ -7,7 +7,7 @@
 
 <p><a class="logo" href="//whatwg.org/"><img height="100" src="//resources.whatwg.org/logo-fetch.svg" width="100" alt="WHATWG"></a>
 <h1 id="cors">Fetch</h1>
-<h2 class="no-num no-toc" id="living-standard-—-last-updated-20-january-2015">Living Standard — Last Updated 20 January 2015</h2>
+<h2 class="no-num no-toc" id="living-standard-—-last-updated-27-january-2015">Living Standard — Last Updated 27 January 2015</h2>
 
 <dl>
  <dt>Participate:
@@ -3145,6 +3145,7 @@ <h3 id="response-class"><span class="secno">5.4 </span>Response class</h3>
 
   readonly attribute USVString <a title="dom-Response-url" href="#dom-response-url">url</a>;
   readonly attribute unsigned short <a title="dom-Response-status" href="#dom-response-status">status</a>;
+  readonly attribute boolean <a title="dom-Response-ok" href="#dom-response-ok">ok</a>;
   readonly attribute ByteString <a title="dom-Response-statusText" href="#dom-response-statustext">statusText</a>;
   [SameObject] readonly attribute <a href="#headers">Headers</a> <a title="dom-Response-headers" href="#dom-response-headers">headers</a>;
 
@@ -3303,6 +3304,11 @@ <h3 id="response-class"><span class="secno">5.4 </span>Response class</h3>
 return <a title="concept-Response-response" href="#concept-response-response">response</a>'s
 <a title="concept-response-status" href="#concept-response-status">status</a>.
 
+<p>The <dfn title="dom-Response-ok" id="dom-response-ok"><code>ok</code></dfn> attribute's getter must
+return true if <a title="concept-Response-response" href="#concept-response-response">response</a>'s
+<a title="concept-response-status" href="#concept-response-status">status</a> is in the range 200 to 299, and false
+otherwise.
+
 <p>The <dfn title="dom-Response-statusText" id="dom-response-statustext"><code>statusText</code></dfn> attribute's getter
 must return <a title="concept-Response-response" href="#concept-response-response">response</a>'s
 <a title="concept-response-status-message" href="#concept-response-status-message">status message</a>.
@@ -3587,6 +3593,7 @@ <h2 class="no-num" id="acknowledgments">Acknowledgments</h2>
 Mark Nottingham,
 Mark S. Miller,
 Martin Dürst,
+Matt Andrews,
 Matt Falkenhagen,
 Matt Oshry,
 Matt Womer,

Overview.src.html

@@ -3099,6 +3099,7 @@ <h3>Response class</h3>
 
   readonly attribute USVString <span title=dom-Response-url>url</span>;
   readonly attribute unsigned short <span title=dom-Response-status>status</span>;
+  readonly attribute boolean <span title=dom-Response-ok>ok</span>;
   readonly attribute ByteString <span title=dom-Response-statusText>statusText</span>;
   [SameObject] readonly attribute <span>Headers</span> <span title=dom-Response-headers>headers</span>;
 
@@ -3257,6 +3258,11 @@ <h3>Response class</h3>
 return <span title=concept-Response-response>response</span>'s
 <span title=concept-response-status>status</span>.
 
+<p>The <dfn title=dom-Response-ok><code>ok</code></dfn> attribute's getter must
+return true if <span title=concept-Response-response>response</span>'s
+<span title=concept-response-status>status</span> is in the range 200 to 299, and false
+otherwise.
+
 <p>The <dfn title=dom-Response-statusText><code>statusText</code></dfn> attribute's getter
 must return <span title=concept-Response-response>response</span>'s
 <span title=concept-response-status-message>status message</span>.
@@ -3480,6 +3486,7 @@ <h2 class=no-num>Acknowledgments</h2>
 Mark Nottingham,
 Mark S. Miller,
 Martin D&uuml;rst,
+Matt Andrews,
 Matt Falkenhagen,
 Matt Oshry,
 Matt Womer,