Detect and handle the case of our own typo correction extension being installed in parallel

lib/typoFixer.js

Index: lib/typoFixer.js
===================================================================
--- a/lib/typoFixer.js
+++ b/lib/typoFixer.js
@@ -12,27 +12,47 @@
 let appIntegration = require("typoAppIntegration");
 let netError = require("typoNetError");
 
-// Attach our handlers to all browser windows
-new WindowObserver(
+let typoWindowObserver = null;
+
+exports.attachWindowObserver = attachWindowObserver;
+function attachWindowObserver()
 {
-  applyToWindow: function(window)
+  if (typoWindowObserver)
+    return;
+  
+  // Attach our handlers to all browser windows
+  typoWindowObserver = new WindowObserver(
   {
-    if (!appIntegration.isKnownWindow(window))
-      return;
-    
-    netError.applyToWindow(window);
-    appIntegration.applyToWindow(window, correctURL);
-  },
+    applyToWindow: function(window)
+    {
+      if (!appIntegration.isKnownWindow(window))
+        return;
+      
+      netError.applyToWindow(window);
+      appIntegration.applyToWindow(window, correctURL);
+    },
 
-  removeFromWindow: function(window)
-  {
-    if (!appIntegration.isKnownWindow(window))
-      return;
-    
-    netError.removeFromWindow(window);
-    appIntegration.removeFromWindow(window);
-  }
-});
+    removeFromWindow: function(window)
+    {
+      if (!appIntegration.isKnownWindow(window))
+        return;
+      
+      netError.removeFromWindow(window);
+      appIntegration.removeFromWindow(window);
+    }
+  });
+}
+
+exports.detachWindowObserver = detachWindowObserver;
+function detachWindowObserver()
+{
+  if (!typoWindowObserver)
+    return;
+  
+  // Detach our handlers from all browser windows
+  typoWindowObserver.shutdown();
+  typoWindowObserver = null;
+}
 
 function parseURL(url)
 {