Update contentSettings extension API docs.

chrome/common/extensions/docs/samples.json

 {
   "api": {
     "chrome.bookmarks.create": "bookmarks.html#method-create",
     "chrome.bookmarks.export": "bookmarks.html#method-export",
     "chrome.bookmarks.get": "bookmarks.html#method-get",
     "chrome.bookmarks.getChildren": "bookmarks.html#method-getChildren",
     "chrome.bookmarks.getRecent": "bookmarks.html#method-getRecent",
     "chrome.bookmarks.getSubTree": "bookmarks.html#method-getSubTree",
     "chrome.bookmarks.getTree": "bookmarks.html#method-getTree",
     "chrome.bookmarks.import": "bookmarks.html#method-import",
@@ skipping 52 matching lines @@
     "chrome.experimental.devtools.inspectedWindow.reload": "experimental.devtools.inspectedWindow.html#method-reload",
     "chrome.experimental.devtools.network.getHAR": "experimental.devtools.network.html#method-getHAR",
     "chrome.experimental.devtools.network.onNavigated": "experimental.devtools.network.html#event-onNavigated",
     "chrome.experimental.devtools.network.onRequestFinished": "experimental.devtools.network.html#event-onRequestFinished",
     "chrome.experimental.devtools.panels.create": "experimental.devtools.panels.html#method-create",
     "chrome.experimental.devtools.panels.setOpenResourceHandler": "experimental.devtools.panels.html#method-setOpenResourceHandler",
     "chrome.experimental.infobars.show": "experimental.infobars.html#method-show",
     "chrome.experimental.savePage.saveAsMHTML": "experimental.savePage.html#method-saveAsMHTML",
     "chrome.experimental.settings.clear": "experimental.settings.html#method-clear",
     "chrome.experimental.settings.get": "experimental.settings.html#method-get",
+    "chrome.experimental.settings.onChanged": "experimental.settings.html#event-onChanged",
     "chrome.experimental.settings.remove": "experimental.settings.html#method-remove",
     "chrome.experimental.settings.set": "experimental.settings.html#method-set",
     "chrome.experimental.speechInput.isRecording": "experimental.speechInput.html#method-isRecording",
     "chrome.experimental.speechInput.onError": "experimental.speechInput.html#event-onError",
     "chrome.experimental.speechInput.onResult": "experimental.speechInput.html#event-onResult",
     "chrome.experimental.speechInput.onSoundEnd": "experimental.speechInput.html#event-onSoundEnd",
     "chrome.experimental.speechInput.onSoundStart": "experimental.speechInput.html#event-onSoundStart",
     "chrome.experimental.speechInput.start": "experimental.speechInput.html#method-start",
     "chrome.experimental.speechInput.stop": "experimental.speechInput.html#method-stop",
     "chrome.experimental.webRequest.addEventListener": "experimental.webRequest.html#method-addEventListener",
@@ skipping 2262 matching lines @@
       "source_files": [
         "manifest.json",
         "popup.html",
         "sample.css"
       ],
       "source_hash": "c8bfc2b60f25c24dc3c5aaf75dd635c9419df66d",
       "zip_path": "examples\/api\/extension\/isAllowedAccess.zip"
     }
   ]
 }