Implement SetWindowTextAndCaretPos and SetCaretPos on iOS.

Implements the two methods on iOS.

Bug: 726702
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ib2a8a40be00c555096ca79915654d62e6ee1ac77
Reviewed-on: https://chromium-review.googlesource.com/1165085Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584400}

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

@@ -279,11 +279,18 @@ void OmniboxViewIOS::SetWindowTextAndCaretPos(const base::string16& text,
 
   if (notify_text_changed)
     model()->OnChanged();
+
+  SetCaretPos(caret_pos);
 }
 
-// TODO(crbug.com/726702): Implement this and have |SetWindowTextAndCaretPos()|
-// call it.
-void OmniboxViewIOS::SetCaretPos(size_t caret_pos) {}
+void OmniboxViewIOS::SetCaretPos(size_t caret_pos) {
+  DCHECK(caret_pos <= field_.text.length || caret_pos == 0);
+  UITextPosition* start = field_.beginningOfDocument;
+  UITextPosition* newPosition =
+      [field_ positionFromPosition:start offset:caret_pos];
+  field_.selectedTextRange =
+      [field_ textRangeFromPosition:newPosition toPosition:newPosition];
+}
 
 void OmniboxViewIOS::RevertAll() {
   ignore_popup_updates_ = true;