Do not consider event on unfocusable fields

These fields cannot be filled, so ignore event on them.

Test: autofilling shipping address in shop.economist.com
Bug: 
Change-Id: I0c754b61da4c6cadda912ce10dfd2edd43285719
Reviewed-on: https://chromium-review.googlesource.com/749947Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Reviewed-by: Roger McFarlane <rogerm@chromium.org>
Reviewed-by: Peter Lee <pkl@chromium.org>
Reviewed-by: Moe Ahmadi (slow) <mahmadi@chromium.org>
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517411}

components/autofill/ios/browser/autofill_agent.mm

@@ -55,8 +55,9 @@ using FormDataVector = std::vector<autofill::FormData>;
 // |fetchFormsWithName:minimumRequiredFieldsCount:pageURL:completionHandler|
 typedef void (^FetchFormsCompletionHandler)(BOOL, const FormDataVector&);
 
-// Gets the first form and field specified by |fieldName| from |forms|,
-// modifying the returned field so that input elements are also handled.
+// Gets the first focusable form and field specified by |fieldName| from
+// |forms|, modifying the returned field so that input elements are also
+// handled.
 void GetFormAndField(autofill::FormData* form,
                      autofill::FormFieldData* field,
                      const FormDataVector& forms,
@@ -66,7 +67,7 @@ void GetFormAndField(autofill::FormData* form,
   *form = forms[0];
   const base::string16 fieldName16 = base::UTF8ToUTF16(fieldName);
   for (const auto& currentField : form->fields) {
-    if (currentField.name == fieldName16) {
+    if (currentField.name == fieldName16 && currentField.is_focusable) {
       *field = currentField;
       break;
     }