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..5399bb738cae37e9a879742499bad55827f14bdd 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 +41,19 @@ chrome.test.runTests([
   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);
+    });
   }
 ]);