Prevent Google Mail Checker from scheduling more than one concurrent request.

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 962 matching lines @@
         "_locales\/th\/messages.json",
         "_locales\/tr\/messages.json",
         "_locales\/uk\/messages.json",
         "_locales\/vi\/messages.json",
         "_locales\/zh_CN\/messages.json",
         "_locales\/zh_TW\/messages.json",
         "background.html",
         "manifest.json",
         "options.html"
       ],
-      "source_hash": "327e6bf6005b861f17848b59dc50ebb18d1a57f4",
+      "source_hash": "6c4da0f4e9348842619fce0179f3f35ca24027ad",
       "zip_path": "examples\/extensions\/gmail.zip"
     },
     {
       "api_calls": [
         "chrome.extension.getBackgroundPage",
         "chrome.extension.getURL",
         "chrome.tabs.create",
         "chrome.tabs.get",
         "chrome.tabs.getSelected",
         "chrome.tabs.onUpdated",
@@ skipping 882 matching lines @@
       "source_files": [
         "manifest.json",
         "popup.html",
         "sample.css"
       ],
       "source_hash": "c8bfc2b60f25c24dc3c5aaf75dd635c9419df66d",
       "zip_path": "examples\/api\/extension\/isAllowedAccess.zip"
     }
   ]
 }