Added pretty printers for some Ink Drop enums.

ui/views/animation/ink_drop_animation_ended_reason.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 "ui/views/animation/ink_drop_animation_ended_reason.h"
 
 #include "base/logging.h"
 
 namespace views {
 
-std::string ToString(InkDropAnimationEndedReason reason) {
+std::string ToString(const InkDropAnimationEndedReason& reason) {
   switch (reason) {
     case InkDropAnimationEndedReason::SUCCESS:
       return "SUCCESS";
     case InkDropAnimationEndedReason::PRE_EMPTED:
       return "PRE_EMPTED";
   }
   NOTREACHED()
       << "Should never be reached but is necessary for some compilers.";
   return std::string();
 }
 
 }  // namespace views