Move ReadFileToString to the base namespace.

base/process/process_iterator_linux.cc

Index: base/process/process_iterator_linux.cc
diff --git a/base/process/process_iterator_linux.cc b/base/process/process_iterator_linux.cc
index 6da51ca3b55399b2ccd7867de39acb014d9e4815..0587d7b88c59daae372adc154030461a66f9f07f 100644
--- a/base/process/process_iterator_linux.cc
+++ b/base/process/process_iterator_linux.cc
@@ -44,7 +44,7 @@ bool GetProcCmdline(pid_t pid, std::vector<std::string>* proc_cmd_line_args) {
 
   FilePath cmd_line_file = internal::GetProcPidDir(pid).Append("cmdline");
   std::string cmd_line;
-  if (!file_util::ReadFileToString(cmd_line_file, &cmd_line))
+  if (!ReadFileToString(cmd_line_file, &cmd_line))
     return false;
   std::string delimiters;
   delimiters.push_back('\0');