Add base:: namespace to straggling string16s left in chrome/browser/ui.

chrome/browser/ui/browser.cc

Index: chrome/browser/ui/browser.cc
diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index eaa47a6846c89f747e10a8e54e00a8398cc8b62c..fac96ff471e9f41932fa1e621c79a15e30c6124a 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -1153,8 +1153,8 @@ void Browser::OverscrollUpdate(int delta_y) {
 
 void Browser::ShowValidationMessage(content::WebContents* web_contents,
                                     const gfx::Rect& anchor_in_root_view,
-                                    const string16& main_text,
-                                    const string16& sub_text) {
+                                    const base::string16& main_text,
+                                    const base::string16& sub_text) {
   RenderWidgetHostView* rwhv = web_contents->GetRenderWidgetHostView();
   if (rwhv) {
     validation_message_bubble_ =