Change WebBluetooth chooser OK button's label to be "Pair"

chrome/browser/chooser_controller/mock_chooser_controller.cc

 // Copyright 2016 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/chooser_controller/mock_chooser_controller.h"
 
 MockChooserController::MockChooserController(content::RenderFrameHost* owner)
     : ChooserController(owner) {}
 
 MockChooserController::~MockChooserController() {}
 
+base::string16 MockChooserController::GetOkButtonLabel() const {
+  return base::string16();
+}
+
 size_t MockChooserController::NumOptions() const {
   return option_names_.size();
 }
 
 base::string16 MockChooserController::GetOption(size_t index) const {
   return option_names_[index];
 }
 
 void MockChooserController::OptionAdded(const base::string16 option_name) {
   option_names_.push_back(option_name);
   if (observer())
     observer()->OnOptionAdded(option_names_.size() - 1);
 }
 
 void MockChooserController::OptionRemoved(const base::string16 option_name) {
   for (auto it = option_names_.begin(); it != option_names_.end(); ++it) {
     if (*it == option_name) {
       size_t index = it - option_names_.begin();
       option_names_.erase(it);
       if (observer())
         observer()->OnOptionRemoved(index);
       return;
     }
   }
 }