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..592a472ba3f8801613653bcebf57fffacd611920 100644
--- a/go-back-with-backspace/content_script.js
+++ b/go-back-with-backspace/content_script.js
@@ -12,9 +12,7 @@ chrome.storage.sync.get({
   whitelist: []
 }, function(items) {
   options = items;
-  window.addEventListener('keydown', function(e) {
-    handleBackspace(e);
-  });
+  window.addEventListener('keydown', handleBackspace);
 });
 
 // Update the local options when they're changed externally.
@@ -36,7 +34,8 @@ 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.
@@ -55,8 +54,27 @@ function handleBackspace(e) {
   if (isEditable(document.activeElement))
     return;
 
-  e.shiftKey ? window.history.forward(): window.history.back();
-  e.preventDefault();
+  // Make sure this extension is still active.
+  // sendMessage throws an internal error, not reported in lastError, if the
+  // other end no longer exists. So we use JS error-catching rather than
+  // extension errors.

[Devlin, 2016/09/27 16:08:57]

please add a crbug.com/nnn here.

[Pam (message me for reviews), 2016/09/27 23:37:32]

I'll take that as confirmation that it's not intended behavior. Done.

+  try {
+    chrome.runtime.sendMessage('', function(response) {

[Devlin, 2016/09/27 16:08:57]

shouldn't need ''

[Pam (message me for reviews), 2016/09/27 23:37:32]

That's the message, which is not optional. If it should be, let me know and I'll
file a bug for it.

[Devlin, 2016/09/29 20:55:34]

Whoops, you're right.  This is fine.

+      // Future-proofing in case sendMessage ever changes to setting lastError
+      // instead of throwing a JS error.
+      if (chrome.runtime.lastError) {
+        window.removeEventListener('keydown', handleBackspace);
+      } else {
+        e.shiftKey ? window.history.forward(): window.history.back();
+        e.preventDefault();
+      }
+    });
+  } catch(error) {
+    // If we have no connection to the background page, the extension has
+    // been updated, disabled, or uninstalled. Remove our listener and do
+    // nothing.
+    window.removeEventListener('keydown', handleBackspace);
+  }
 }
 
 // Return true if the option to disable the extension in applets is enabled,
@@ -69,8 +87,11 @@ 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;