Update references to the extension messaging APIs to point to the "runtime"

chrome/common/extensions/docs/templates/intros/privacy.html

 <p id="classSummary">
   Use the <code>chrome.privacy</code> module to control usage of the features in
   Chrome that can affect a user's privacy. This module relies on the
   <a href="types.html#ChromeSetting">ChromeSetting prototype of the type API</a>
   for getting and setting Chrome's configuration.
 </p>
 
 <p class="note">
   The <a href="http://www.google.com/intl/en/landing/chrome/google-chrome-privacy-whitepaper.pdf">Chrome Privacy Whitepaper</a>
   gives background detail regarding the features which this API can control.
@@ skipping 55 matching lines @@
   This means that you ought to use the <code>get()</code> method to determine
   your level of access, and then only call <code>set()</code> if your extension
   can grab control over the setting (in fact if your extension can't control the
   setting it's probably a good idea to visually disable the functionality to
   reduce user confusion):
 </p>
 
 <pre>chrome.privacy.services.autofillEnabled.get({}, function(details) {
   if (details.levelOfControl === 'controllable_by_this_extension') {
     chrome.privacy.services.autofillEnabled.set({ value: true }, function() {
-      if (chrome.extension.lastError === undefined)
+      if (chrome.runtime.lastError === undefined)
         console.log("Hooray, it worked!");
       else
-        console.log("Sadness!", chrome.extension.lastError);
+        console.log("Sadness!", chrome.runtime.lastError);
     }
   }
 });</pre>
 
 <p>
   If you're interested in changes to a setting's value, add a listener to its
   <code>onChange</code> event. Among other uses, this will allow you to warn the
   user if a more recently installed extension grabs control of a setting, or if
   enterprise policy overrides your control. To listen for changes to Autofill's
   status, for example, the following code would suffice:
@@ skipping 82 matching lines @@
   This means that you ought to use the <code>get()</code> method to determine
   your level of access, and then only call <code>set()</code> if your extension
   can grab control over the setting (in fact if your extension can't control the
   setting it's probably a good idea to visibly disable the functionality to
   reduce user confusion):
 </p>
 
 <pre>chrome.privacy.services.autofillEnabled.get({}, function(details) {
   if (details.levelOfControl === 'controllable_by_this_extension') {
     chrome.privacy.services.autofillEnabled.set({ value: true }, function() {
-      if (chrome.extension.lastError === undefined)
+      if (chrome.runtime.lastError === undefined)
         console.log("Hooray, it worked!");
       else
-        console.log("Sadness!", chrome.extension.lastError);
+        console.log("Sadness!", chrome.runtime.lastError);
     }
   }
 });</pre>
 
 <p>
   If you're interested in changes to a setting's value, add a listener to its
   <code>onChange</code> event. Among other uses, this will allow you to warn the
   user if a more recently installed extension grabs control of a setting, or if
   enterprise policy overrides your control. To listen for changes to Autofill's
   status, for example, the following code would suffice:
 </p>
 
 <pre>chrome.privacy.services.autofillEnabled.onChange.addListener(
     function (details) {
       // The new value is stored in `details.value`, the new level of control
       // in `details.levelOfControl`, and `details.incognitoSpecific` will be
       // `true` if the value is specific to Incognito mode.
     });</pre>
 
 <h2 id="examples">Examples</h2>
 <p>
   For example code, see the
   <a href="samples.html#privacy">Privacy API samples</a>.
-</p>
+</p>