[omnibox] Break out SetCaretPos() method and enhance browser test

ios/chrome/browser/ui/omnibox/omnibox_view_ios.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ios/chrome/browser/ui/omnibox/omnibox_view_ios.h"
 
 #import <CoreText/CoreText.h>
 #import <MobileCoreServices/MobileCoreServices.h>
 
 #include "base/auto_reset.h"
@@ skipping 224 matching lines @@
   NSAttributedString* as = ApplyTextAttributes(text);
   [field_ setText:as userTextLength:[as length]];
 
   if (update_popup)
     UpdatePopup();
 
   if (notify_text_changed)
     model()->OnChanged();
 }
 
+void OmniboxViewIOS::SetCaretPos(size_t caret_pos) {}

[Peter Kasting, 2017/05/18 18:38:34]

Is this NOTIMPLEMENTED(), or is there a reason why on iOS it makes no logical
sense to set the caret position?  I'm worried about the lack of that causing
potential security/usability bugs on iOS.  It seems like maybe support for this
needs to be added (separately).

[Kevin Bailey, 2017/05/18 19:48:17]

I assume this is for Rohit? You saw his comment?

[Peter Kasting, 2017/05/18 19:50:10]

Yes.

[rohitrao (ping after 24h), 2017/05/23 14:02:39]

This used to be impossible with the APIs that iOS provided.  It's possible to
implement now, but "caret position" only has meaning when the omnibox is
focused.

Does anyone know what scenarios cause SetCaretPos() to be called?  I remember
this being used mostly for Instant, so at one point it never really got called
on iOS.

[Kevin Bailey, 2017/05/23 14:16:19]

SetWindowTextAndCaretPos() is called during most any change to the Omnibox,
except single character entry, which the Textfield takes care of itself.
SetCaretPos() is a new function that we just added for when we only need to
update the caret. Currently, it's only called from OmniboxEditModel::Revert().

+
 void OmniboxViewIOS::RevertAll() {
   ignore_popup_updates_ = true;
   OmniboxView::RevertAll();
   ignore_popup_updates_ = false;
 }
 
 void OmniboxViewIOS::UpdatePopup() {
   model()->SetInputInProgress(true);
 
   if (!model()->has_focus())
@@ skipping 630 matching lines @@
 // is being left out for now because it was not present before the OmniboxView
 // rewrite.
 #if 0
   // When editing is in progress, the url text is not colored, so there is
   // nothing to emphasize.  (Calling SetText() in that situation would also be
   // harmful, as it would reset the carat position to the end of the text.)
   if (!IsEditingOrEmpty())
     SetText(GetText());
 #endif
 }