Support persistent incognito preferences

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

 <div id="pageData-name" class="pageData">Preferences</div>
 
 <!-- BEGIN AUTHORED CONTENT -->
 <p id="classSummary">
 The <code>chrome.preferences</code> module contains a prototype for giving other
-modules access to manage preferences stored by Chrome. This prototype is used
-for example for <a
+modules access to manage Chrome's preferences. This prototype is used for
+example for <a
   href="proxy.html#property-settings"><code>chrome.proxy.settings</code></a>.
 </p>
 
-<h2 id="description">Overview</h2>
+<h2 id="description">Functions</h2>
 
 <p>
-The preferences API provides a common set of functions
+The preferences API provides a commen set of functions
 (<code>getEffective()</code>, <code>set()</code>, and <code>clear()</code>) as
 well as an event publisher (<code>onChangeEffective</code>) for various
 preferences in Chrome. The <a href="proxy.html#overview-examples">proxy settings
  examples</a> demonstrate how these functions are intended to be used.
 </p>
 
-<!--
 <h2 id="lifecycle">Life cycle of preferences</h2>
 
 <p>
 The life cycle of preferences depends on whether they are set for regular or
-incognito profiles. </p>
--->
+incognito profiles. Currently, preferences can only be set for regular profiles.
+</p>
 
 <p>
-Currently, preferences can only be set for regular profiles. Once set, they
+Preferences for <em>regular profiles</em> are persisted to disk. Once set, they
 remain in place until they are cleared by the governing extension, or the
 governing extension is disabled or uninstalled.
 </p>
 
 <h2 id="precedence">Precedence</h2>
 
 <p>
 Chrome manages preferences on different layers. The following list describes the
 layers that may influence the effective preferences, in increasing order of
 precedence.
 <ol>
   <li>System preferences provided by the operating system</li>
-  <li>Command-line parameters</li>
+  <li>Command line parameters</li>
   <li>Preferences set by extensions</li>
   <li>Policies</li>
 </ol>
 </p>
 
 <p>
 As the list implies, policies might overrule any changes that you specify with
 your extension.
 </p>
 
@@ skipping 13 matching lines @@
   <li>If only <b>(I)</b> is set, these preferences are effective for only
   incognito windows. Regular windows use the preferences determined by the lower
   layers (command-line options and system settings).</li>
   <li>If both <b>(R)</b> and <b>(I)</b> are set, the respective preferences are
   used for regular and incognito windows.</li>
 </ul>
 </p>
 -->
 
 <p>
-If two or more extensions want to set the same preference to different values,
-the extension installed most recently takes precedence over the other
-extensions.
+If two extensions want to set the same preference to different values, the
+extension installed last takes precedence over the other extensions.
 <!-- If the
 extension installed last sets only <b>(I)</b>, the preference of regular windows
 can be defined by previously installed extensions. -->
 </p>
 
 <p>
 The <em>effective</em> preference value is the setting that results from
 considering the preference rules. It is used by Chrome.
 <p>
 
 <!-- END AUTHORED CONTENT -->