Inject automatically on install etc., add mime types, and fix nits.

go-back-with-backspace/content_script.js

Index: go-back-with-backspace/content_script.js
diff --git a/go-back-with-backspace/content_script.js b/go-back-with-backspace/content_script.js
index f80ab2a2b3eab5adedfd2c31ba8c9b1ea571fe0c..820ed255e271501a8fb628eb1fc8aac8c75ec22d 100644
--- a/go-back-with-backspace/content_script.js
+++ b/go-back-with-backspace/content_script.js
@@ -12,8 +12,14 @@ chrome.storage.sync.get({
   whitelist: []
 }, function(items) {
   options = items;
-  window.addEventListener('keydown', function(e) {
-    handleBackspace(e);
+  window.addEventListener('keydown', handleBackspace);
+
+  // Set up a longstanding connection to the background page. When the
+  // extension updates, is disabled, or is uninstalled, this connection will
+  // drop, and we will know to remove the listener.
+  var port = chrome.runtime.connect();
+  port.onDisconnect.addListener(function(port) {
+    window.removeEventListener('keydown', handleBackspace);
   });
 });
 
@@ -36,7 +42,8 @@ function handleBackspace(e) {
       e.key !== 'Backspace' ||
       e.altKey ||
       e.ctrlKey ||
-      e.metaKey)
+      e.metaKey ||
+      window.history.length < 2) // Nowhere to go back or forward to anyway.
     return;
 
   // The blacklist overrides everything.
@@ -69,8 +76,11 @@ function disabledInApplet(target) {
   var nodeType = target.type || '';
   nodeType = nodeType.toLowerCase();
   if ((nodeName === 'EMBED' || nodeName === 'OBJECT') &&
-      (nodeType === 'application/x-shockwave-flash' ||
-       nodeType === 'application/java')) {
+      (nodeType === 'application/java' ||
+       nodeType === 'application/pdf' ||
+       nodeType === 'application/x-chat' ||
+       nodeType === 'application/x-google-chrome-pdf' ||
+       nodeType === 'application/x-shockwave-flash')) {
     return true;
   }
   return false;