Fix outdated documentation on blocking start and handling of synchronous requests

chrome/common/extensions/docs/static/webRequest.html

 <div id="pageData-name" class="pageData">Web Requests</div>
 
 <!-- BEGIN AUTHORED CONTENT -->
 <p id="classSummary">
 Use the <code>chrome.webRequest</code> module to intercept, block,
 or modify requests in-flight and to observe and analyze traffic.
 </p>
 
 <h2 id="manifest">Manifest</h2>
 <p>You must declare the "webRequest" permission in the <a
   href="manifest.html">extension manifest</a> to use the web request
 API, along with <a href="manifest.html#permissions">host permissions</a>
 for any hosts whose network requests you want to access. If you want to
 use the web request API in a blocking fashion, you need to request
 the "webRequestBlocking" permission in addition.
 For example:</p>
 <pre>{
   "name": "My extension",
   ...
   <b>"permissions": [
     "webRequest",
     "*://*.google.com"
   ]</b>,
   ...
 }</pre>
 
-<p class="note">
-<b>Node:</b> If you request the "webRequestBlocking" permission, web requests
-are delayed until the background page of your extension has been loaded. This
-allows you to register event listeners before any web requests are processed.
-In order to avoid deadlocks, you must not start synchronous XmlHttpRequests or
-include scripts from the internet via <code>&lt;script src="..."&gt;</code> tags
-in your background page.
-</p>
-
 <h2 id="life_cycle">Life cycle of requests</h2>
 
 <p>
 The web request API defines a set of events that follow the life cycle of a web
 request. You can use these events to observe and analyze traffic. Certain
 synchronous events will allow you to intercept, block, or modify a request.
 </p>
 
 <p>
 The event life cycle for successful requests is illustrated here, followed by
@@ skipping 91 matching lines @@
 <code>https://</code>,
 <code>ftp://</code>,
 <code>file://</code>, or
 <code>chrome-extension://</code>.
 In addition, even certain requests with URLs using one of the above schemes
 are hidden, e.g.,
 <code>chrome-extension://other_extension_id</code> where
 <code>other_extension_id</code> is not the ID of the extension to handle
 the request,
 <code>https://www.google.com/chrome</code>,
-and others (this list is not complete).
+and others (this list is not complete). Also synchronous XMLHttpRequests from
+your extension are hidden from blocking event handlers in order to prevent
+deadlocks.
 </p>
 
 <h2 id="concepts">Concepts</h2>
 
 <p>As the following sections explain, events in the web request API use request
 IDs, and you can optionally specify filters and extra information when you
 register event listeners.</p>
 
 <h3 id="Request IDs">Request IDs</h3>
 
@@ skipping 143 matching lines @@
     }
     return {requestHeaders: details.requestHeaders};
   },
   {urls: ["&lt;all_urls&gt;"]},
   ["blocking", "requestHeaders"]);
 </pre>
 
 <p> For more example code, see the <a href="samples.html#webrequest">web request
 samples</a>.</p>
 <!-- END AUTHORED CONTENT -->