Clean up error handling logic for extension tab muting

chrome/test/data/extensions/api_test/tabs/basics/muted.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 var testTabId_;
 
 chrome.test.runTests([
   function setupWindow() {
     chrome.tabs.getCurrent(pass(function(tab) {
       testTabId_ = tab.id;
@@ skipping 12 matching lines @@
       }));
     }));
   },
 
   function makeMuted() {
     onUpdatedExpect("muted", true, {mutedCause: chrome.runtime.id});
     chrome.tabs.update(testTabId_, {muted: true}, pass());
   },
 
   function testStaysMutedAfterChangingWindow() {
-    chrome.windows.create({}, pass(function(window)
-    {
+    chrome.windows.create({}, pass(function(window) {
       chrome.tabs.move(testTabId_, {windowId: window.id, index: -1},
                        pass(function(tab) {
         assertEq(true, tab.muted);
       }));
     }));
   },
 
   function makeNotMuted() {
     onUpdatedExpect("muted", false, {mutedCause: chrome.runtime.id});
     chrome.tabs.update(testTabId_, {muted: false}, pass());
+  },
+
+  // Prior tests in this file have already toggled the muted state twice.
+  // We update a third (and final) time before rate limiting kicks in.
+  // (except rate limiting is ignored when we set muted/mutedCause to
+  // the same values.)
+  function frequentRequestsRateLimited() {
+    chrome.tabs.update(testTabId_, {muted: true}, pass());
+    chrome.tabs.update(testTabId_, {muted: true}, pass()); // ignored
+    chrome.tabs.update(testTabId_, {muted: false}, function(tab) {
+      var errMsg = "Rate limit exceeded when updating mute state for tab " +
+        testTabId_ + ".";
+      chrome.test.assertLastError(errMsg);
+    });
   }
 ]);