Use a direct include of strings headers in ppapi/, printing/.

ppapi/native_client/src/trusted/plugin/pnacl_options.cc

Index: ppapi/native_client/src/trusted/plugin/pnacl_options.cc
diff --git a/ppapi/native_client/src/trusted/plugin/pnacl_options.cc b/ppapi/native_client/src/trusted/plugin/pnacl_options.cc
index 05eecf27bf6d8a01bc70d44eac60ef0c8cc90207..ad31e88cce18da5e95acdbd7da6fcd7c6a9cf23d 100644
--- a/ppapi/native_client/src/trusted/plugin/pnacl_options.cc
+++ b/ppapi/native_client/src/trusted/plugin/pnacl_options.cc
@@ -45,7 +45,7 @@ std::vector<char> PnaclOptions::GetOptCommandline() {
   std::vector<nacl::string> tokens;
 
   // Split the experimental_flags_ + the -On along whitespace.
-  // Mostly a copy of "base/string_util.h", but avoid importing
+  // Mostly a copy of "base/strings/string_util.h", but avoid importing
   // base into the PPAPI plugin for now.
   nacl::string delim(" ");
   nacl::string str = experimental_flags_;