Merge birch to m-c.

b2g/chrome/content/forms.js

@@ -185,6 +185,7 @@ let FormAssistant = {
     addEventListener("resize", this, true, false);
     addEventListener("submit", this, true, false);
     addEventListener("pagehide", this, true, false);
+    addEventListener("beforeunload", this, true, false);
     addEventListener("input", this, true, false);
     addEventListener("keydown", this, true, false);
     addMessageListener("Forms:Select:Choice", this);
@@ -292,7 +293,9 @@ let FormAssistant = {
         break;
 
       case "pagehide":
-        // We are only interested to the pagehide event from the root document.
+      case "beforeunload":
+        // We are only interested to the pagehide and beforeunload events from
+        // the root document.
         if (target && target != content.document) {
           break;
         }