Clean up error handling logic for extension tab muting

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

Index: chrome/test/data/extensions/api_test/tabs/basics/muted.js
diff --git a/chrome/test/data/extensions/api_test/tabs/basics/muted.js b/chrome/test/data/extensions/api_test/tabs/basics/muted.js
index 6487325f95811273a99361c1bd3ae46b0da954c8..eb004fb4dc11ae84ad6b27898dc2ab42a175aff0 100644
--- a/chrome/test/data/extensions/api_test/tabs/basics/muted.js
+++ b/chrome/test/data/extensions/api_test/tabs/basics/muted.js
@@ -30,8 +30,7 @@ chrome.test.runTests([
   },
 
   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);
@@ -42,5 +41,12 @@ chrome.test.runTests([
   function makeNotMuted() {
     onUpdatedExpect("muted", false, {mutedCause: chrome.runtime.id});
     chrome.tabs.update(testTabId_, {muted: false}, pass());
+  },
+
+  function frequentRequestsRateLimited() {
+    chrome.tabs.update(testTabId_, {muted: true}, pass());

[miu, 2015/07/16 00:28:26]

Please add a comment at the top of this function that mentions prior tests in
this file have already toggled the mute state twice, and that this update() will
be the third (and final) time before rate limiting should kick in.

+    chrome.tabs.update(testTabId_, {muted: false}, function(tab) {
+      assertEq(true, tab.muted); // state not updated since rate limited

[miu, 2015/07/16 00:28:26]

For completeness, consider adding:

  assertTrue(!!chrome.runtime.lastError);
  if (chrome.runtime.lastError) {
    assertEq("<ERROR MESSAGE FOR RATE LIMITING HERE>",
chrome.runtime.lastError.message);
  }

+    });
   }
 ]);