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

chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.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 "chrome/browser/ui/cocoa/omnibox/omnibox_view_mac.h"
 
 #include <Carbon/Carbon.h>  // kVK_Return
 
 #include "base/auto_reset.h"
 #include "base/mac/foundation_util.h"
@@ skipping 335 matching lines @@
   DCHECK_LE(caret_pos, text.size());
   SetTextAndSelectedRange(text, NSMakeRange(caret_pos, 0));
 
   if (update_popup)
     UpdatePopup();
 
   if (notify_text_changed)
     TextChanged();
 }
 
+void OmniboxViewMac::SetCaretPos(size_t caret_pos) {
+  size_t pos = std::min(caret_pos, GetTextLength());
+  SetSelectedRange(NSMakeRange(pos, 0));
+}
+
 void OmniboxViewMac::EnterKeywordModeForDefaultSearchProvider() {
   // We need to do this first, else |SetSelectedRange()| won't work.
   FocusLocation(true);
 
   // Transition the user into keyword mode using their default search provider.
   model()->EnterKeywordModeForDefaultSearchProvider(
       KeywordModeEntryMethod::KEYBOARD_SHORTCUT);
 }
 
 bool OmniboxViewMac::IsSelectAll() const {
@@ skipping 728 matching lines @@
                               display_text);
   NSDictionary* notification_info = @{
       NSAccessibilityAnnouncementKey : announcement,
       NSAccessibilityPriorityKey :     @(NSAccessibilityPriorityHigh)
   };
   NSAccessibilityPostNotificationWithUserInfo(
       [field_ window],
       NSAccessibilityAnnouncementRequestedNotification,
       notification_info);
 }