Use container::back() and container::pop_back().

storage/common/fileapi/file_system_util.cc

Index: storage/common/fileapi/file_system_util.cc
diff --git a/storage/common/fileapi/file_system_util.cc b/storage/common/fileapi/file_system_util.cc
index 3bb9b14f4f427ad08f9ea0879d17b36e9e9fb1c6..f3d7ddbfac3a42669b417ebfb48379710e59795b 100644
--- a/storage/common/fileapi/file_system_util.cc
+++ b/storage/common/fileapi/file_system_util.cc
@@ -38,7 +38,7 @@ base::FilePath VirtualPath::BaseName(const base::FilePath& virtual_path) {
 
   // Keep everything after the final separator, but if the pathname is only
   // one character and it's a separator, leave it alone.
-  while (path.size() > 1 && base::FilePath::IsSeparator(path[path.size() - 1]))
+  while (path.size() > 1 && base::FilePath::IsSeparator(path.back()))
     path.resize(path.size() - 1);
   base::FilePath::StringType::size_type last_separator =
       path.find_last_of(base::FilePath::kSeparators);
@@ -57,7 +57,7 @@ base::FilePath VirtualPath::DirName(const base::FilePath& virtual_path) {
   // that this version never cares about '//' or drive-letters even on win32.
 
   // Strip trailing separators.
-  while (path.size() > 1 && base::FilePath::IsSeparator(path[path.size() - 1]))
+  while (path.size() > 1 && base::FilePath::IsSeparator(path.back()))
     path.resize(path.size() - 1);
 
   StringType::size_type last_separator =
@@ -74,7 +74,7 @@ base::FilePath VirtualPath::DirName(const base::FilePath& virtual_path) {
   path.resize(last_separator);
 
   // Strip trailing separators.
-  while (path.size() > 1 && base::FilePath::IsSeparator(path[path.size() - 1]))
+  while (path.size() > 1 && base::FilePath::IsSeparator(path.back()))
     path.resize(path.size() - 1);
 
   if (path.empty())