Look at e.path where available (M55+)

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 ea6cecb9faed2c4f69ea92af858ad7961f53eac5..1e41c87bd97bca582a3f344b68ee7f440877f841 100644
--- a/go-back-with-backspace/content_script.js
+++ b/go-back-with-backspace/content_script.js
@@ -2,17 +2,21 @@
 // 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 (see
-  // http://crbug.com/645527), so we'll have to look at the focused (active)
-  // element. This means it will not work properly with shadow DOM.
-  // TODO: Fix behavior with shadow DOM when the above bug is resolved.
+  // Before Chrome 55, listening on the Window means the event has no path,
+  // instead pointing to the Window (see http://crbug.com/645527). In that
+  // case, we have to look at the focused (active) element.
+  // TODO: Switch entirely to e.path once Chrome 55 is launched.
   if (e.key === 'Backspace' &&
       !e.defaultPrevented &&
       !e.altKey &&
       !e.ctrlKey &&
-      !e.metaKey &&
-      !isEditable(document.activeElement)) {
-    e.shiftKey ? window.history.forward(): window.history.back();
-    e.preventDefault();
+      !e.metaKey) {
+    var target = e.path[0];
+    if (target === window)
+      target = document.activeElement;
+    if (!isEditable(target)) {
+      e.shiftKey ? window.history.forward(): window.history.back();
+      e.preventDefault();
+    }
   }
 });