Prevent extensions from clobbering JSON implementation that extension calls use

chrome/test/data/extensions/api_test/messaging/connect/test.html

 <script>
+JSON.parse = function() {
+  return "JSON.parse clobbered by extension.";
+}
+
+JSON.stringify = function() {
+  return "JSON.stringify clobbered by extension.";
+}
+
+Array.prototype.toJSON = function() {
+  return "Array.prototype.toJSON clobbered by extension.";
+}
+
+Object.prototype.toJSON = function() {
+  return "Object.prototype.toJSON clobbered by extension.";
+}
+
 // Keep track of the tab that we're running tests in, for simplicity.
 var testTab = null;
   
 chrome.test.runTests([
   function setupTestTab() {
     chrome.test.log("Creating tab...");
     chrome.tabs.create({
       url: "http://localhost:1337/files/extensions/test_file.html"
     }, function(tab) {
       chrome.tabs.onUpdated.addListener(function listener(tabid, info) {
@@ skipping 94 matching lines @@
     var port = chrome.tabs.connect(testTab.id);
     port.postMessage({testDisconnectOnClose: true});
     port.onDisconnect.addListener(function() {
       chrome.test.succeed();
       testTab = null; // the tab is about:blank now.
     });
   },
 ]);
 
 </script>