Remove const qualifier from function return type.

ash/system/tray/system_tray_delegate.cc

Index: ash/system/tray/system_tray_delegate.cc
diff --git a/ash/system/tray/system_tray_delegate.cc b/ash/system/tray/system_tray_delegate.cc
index 19a7c7e82d463e0ad25b3a3a51a2c720eaeff2bd..314817eefe5aa2137d6b84a4f43ee7a0486fda4b 100644
--- a/ash/system/tray/system_tray_delegate.cc
+++ b/ash/system/tray/system_tray_delegate.cc
@@ -71,19 +71,19 @@ std::string SystemTrayDelegate::GetEnterpriseDomain() const {
   return std::string();
 }
 
-const base::string16 SystemTrayDelegate::GetEnterpriseMessage() const {
+base::string16 SystemTrayDelegate::GetEnterpriseMessage() const {
   return base::string16();
 }
 
-const std::string SystemTrayDelegate::GetSupervisedUserManager() const {
+std::string SystemTrayDelegate::GetSupervisedUserManager() const {
   return std::string();
 }
 
-const base::string16 SystemTrayDelegate::GetSupervisedUserManagerName() const {
+base::string16 SystemTrayDelegate::GetSupervisedUserManagerName() const {
   return base::string16();
 }
 
-const base::string16 SystemTrayDelegate::GetSupervisedUserMessage() const {
+base::string16 SystemTrayDelegate::GetSupervisedUserMessage() const {
   return base::string16();
 }