Add placeholder text to UI Refresh omnibox.

Adds placeholder text to the omnibox.

Bug: 821814
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I48efe7c94afd4ed929b2020f8c68e4031376fea8
Reviewed-on: https://chromium-review.googlesource.com/1064411
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#561042}

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

@@ -4,8 +4,10 @@
 
 #import "ios/chrome/browser/ui/omnibox/omnibox_view_controller.h"
 
+#include "components/strings/grit/components_strings.h"
 #import "ios/chrome/browser/ui/omnibox/omnibox_container_view.h"
 #include "ios/chrome/browser/ui/ui_util.h"
+#include "ui/base/l10n/l10n_util.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
@@ -58,6 +60,7 @@
 - (void)viewDidLoad {
   [super viewDidLoad];
   [self.view setLeadingImageHidden:!IsIPadIdiom()];
+  self.textField.placeholder = l10n_util::GetNSString(IDS_OMNIBOX_EMPTY_HINT);
 }
 
 #pragma mark - public methods