Allow "internal" APIs to be specified in extension API schemas.

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

 <link rel="stylesheet" href="css/samples.css" />
 <script jscontent="search_data"></script>
 <script src="js/sample_search.js"></script>
 
 <script type="text/prerenderjs">
   /**
    * The following code is executed before the jstemplate in this file is
    * rendered, meaning it can modify template data by changing the pageData
    * window variable.  See api_page_generator.js for more information.
    *
    * Adds the samples manifest data + API modules.
    */
   pageData.samples = samples;
   pageData.api_mapping = apiMapping;
   pageData.api_modules = [];
   schema.forEach(function(mod) {
-    if (mod.nodoc) {
-      return;
-    }
-    if (mod.namespace.indexOf('experimental') != -1) {
+    if (mod.nodoc ||
+        mod.internal ||
+        mod.namespace.indexOf('experimental') != -1) {
       return;
     }
     pageData.api_modules.push('chrome.' + mod.namespace);
   });
   pageData.api_modules.push('chrome.experimental');
   pageData.api_modules.sort();
 
   var search_data = {};
   samples.forEach(function(sample) {
     search_data[sample.id] = sample.search_string;
@@ skipping 79 matching lines @@
     <!-- Only show the Install CRX link if a CRX file is provided -->
     <span jsdisplay="$this.crx_path != null">
     - <a jsvalues="href:$this.crx_path">Install extension</a>
     </span>
   </div>
 </div>
 
 <div id="noresults" style="display:none">
   Sorry, no results were found.
 </div>