[iOS] Exit omnibox preedit state on suggestion append.

Exits the preedit state upon appending a suggestion.

Bug: 859011
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I65809145b1f846157b24e1cc0b74035f235f834f
Reviewed-on: https://chromium-review.googlesource.com/1120025
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572547}

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

@@ -983,6 +983,9 @@ void OmniboxViewIOS::OnPopupDidScroll() {
 }
 
 void OmniboxViewIOS::OnSelectedMatchForAppending(const base::string16& str) {
+  // Exit preedit state and append the match. Refocus if necessary.
+  if ([field_ isPreEditing])
+    [field_ exitPreEditState];
   this->SetUserText(str);
   this->FocusOmnibox();
 }