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

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

Index: ios/chrome/browser/ui/omnibox/omnibox_view_ios.mm
diff --git a/ios/chrome/browser/ui/omnibox/omnibox_view_ios.mm b/ios/chrome/browser/ui/omnibox/omnibox_view_ios.mm
index 41e447d6a6bc53aaf1d55013eee0c4f300899698..5a4a4c6da958abb5699b6aa96aa537baa7e43eba 100644
--- a/ios/chrome/browser/ui/omnibox/omnibox_view_ios.mm
+++ b/ios/chrome/browser/ui/omnibox/omnibox_view_ios.mm
@@ -242,6 +242,8 @@ void OmniboxViewIOS::SetWindowTextAndCaretPos(const base::string16& text,
     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();