Use IsWebElementVisible consistently

On some places in the autofill code, IsWebElementVisible is used,
on other that function is "inlined".

This CL changes one such inlined call to call IsWebElementVisible
explicitly.

There should be no visible behaviour changes caused by this CL.

Bug: 833838
Change-Id: Ia0efb92d1a2b781467af929848c8999d8bb72d34
Reviewed-on: https://chromium-review.googlesource.com/1017202Reviewed-by: Roger McFarlane <rogerm@chromium.org>
Commit-Queue: Vaclav Brozek <vabr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553159}

components/autofill/content/renderer/form_autofill_util.cc

@@ -1501,8 +1501,7 @@ void WebFormControlElementToFormField(
       IsTextAreaElement(element) ||
       IsSelectElement(element)) {
     field->is_autofilled = element.IsAutofilled();
-    if (!g_prevent_layout)
-      field->is_focusable = element.IsFocusable();
+    field->is_focusable = IsWebElementVisible(element);
     field->should_autocomplete = element.AutoComplete();
 
     // Use 'text-align: left|right' if set or 'direction' otherwise.