Attach to window, add some editable markers, and add a license file.

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 32fff927f8e80fe94fee0fc0c711ce42554a484f..ba90ed7b77d216a3357fb64941dbd115edd1da42 100644
--- a/go-back-with-backspace/content_script.js
+++ b/go-back-with-backspace/content_script.js
@@ -1,11 +1,15 @@
 // Listen for shift-backspace or unmodified backspace and navigate if not in
-// an editable field.
-document.addEventListener('keydown', function(e) {
+// an editable field. We capture the event at the Window to let any handlers
+// or listeners registered on the Document have a chance to handle it first.
+window.addEventListener('keydown', function(e) {
+  // Listening on the Window means the event has no path, so we'll have to
+  // look at the focused (active) element.
   if (e.key === 'Backspace' &&
+      !e.defaultPrevented &&
       !e.altKey &&
       !e.ctrlKey &&
       !e.metaKey &&
-      !isEditable(e.path)) {
+      !isEditable(document.activeElement)) {

[ojan, 2016/09/09 18:06:30]

This won't do the right thing with shadow DOM.
 
http://plexode.com/eval3/#s=aekVQXANJVQMbAx1yAUpFHj0DVElCjFgOSVBUVZsfHRByHwMN...

e.path is doing something funky here. We should followup with shadow DOM people
to understand if this is really the right behavior.

In the meantime, I think there's much more content that depends on the issue
you're addressing than content that has text controls in shadow DOM. So, I think
this change is good, but needs a TODO to make work with shadow DOM once we've
worked things out there. Filed crbug.com/645527.

     e.shiftKey ? window.history.forward(): window.history.back();
     e.preventDefault();
   }