Only reset autofill attributes if change is user-initiated.

The isTrusted attribute indicates that the change came from the user.
Use it to make sure we don't unset the autofill attributes when
sending our own "input" event.

Bug: 796224
Change-Id: I7502274ba3dbe7d323382af3d884ded005f79bf0
Reviewed-on: https://chromium-review.googlesource.com/840005Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Elodie Banel <lod@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525993}

components/autofill/ios/browser/resources/autofill_controller.js

@@ -596,11 +596,13 @@ __gCrWeb.autofill['fillForm'] = function(data, forceFillFieldName) {
     __gCrWeb.autofill.styleInjected = true;
   }
 
-  // Remove Autofill styling when control element is edited.
+  // Remove Autofill styling when control element is edited by the user.
   var controlElementInputListener = function(evt) {
-    evt.target.removeAttribute('chrome-autofilled');
-    evt.target.isAutofilled = false;
-    evt.target.removeEventListener('input', controlElementInputListener);
+    if (evt.isTrusted) {
+      evt.target.removeAttribute('chrome-autofilled');
+      evt.target.isAutofilled = false;
+      evt.target.removeEventListener('input', controlElementInputListener);
+    }
   };
 
   var form = __gCrWeb.common.getFormElementFromIdentifier(data.formName);