Cleanup: Pass std::string as const reference if possible

chrome/browser/extensions/api/virtual_keyboard_private/chrome_virtual_keyboard_delegate.cc

 // Copyright 2014 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/extensions/api/virtual_keyboard_private/chrome_virtual_keyboard_delegate.h"
 
 #include <string>
 
 #include "ash/shell.h"
 #include "base/command_line.h"
@@ skipping 16 matching lines @@
 namespace keyboard_api = extensions::api::virtual_keyboard_private;
 
 namespace {
 
 aura::Window* GetKeyboardContainer() {
   keyboard::KeyboardController* controller =
       keyboard::KeyboardController::GetInstance();
   return controller ? controller->GetContainerWindow() : nullptr;
 }
 
-std::string GenerateFeatureFlag(std::string feature, bool enabled) {
+std::string GenerateFeatureFlag(const std::string& feature, bool enabled) {
   return feature + (enabled ? "-enabled" : "-disabled");
 }
 
 keyboard::KeyboardMode getKeyboardModeEnum(keyboard_api::KeyboardMode mode) {
   switch (mode) {
     case keyboard_api::KEYBOARD_MODE_NONE:
       return keyboard::NONE;
     case keyboard_api::KEYBOARD_MODE_FULL_WIDTH:
       return keyboard::FULL_WIDTH;
     case keyboard_api::KEYBOARD_MODE_FLOATING:
@@ skipping 147 matching lines @@
 }
 
 bool ChromeVirtualKeyboardDelegate::IsLanguageSettingsEnabled() {
   return (user_manager::UserManager::Get()->IsUserLoggedIn() &&
           !chromeos::UserAddingScreen::Get()->IsRunning() &&
           !(chromeos::ScreenLocker::default_screen_locker() &&
             chromeos::ScreenLocker::default_screen_locker()->locked()));
 }
 
 }  // namespace extensions