libchromeos: Migrate string_utils from Buffet to libchromeos

BUG=chromium:405714
TEST=USE=buffet ./build_packages

Change-Id: I95d8977aed6ffd718751de058d4cdda3a5395c25
Reviewed-on: https://chromium-review.googlesource.com/213361
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/commands/command_dictionary.cc b/buffet/commands/command_dictionary.cc
index 64f47c1..54753ad 100644
--- a/buffet/commands/command_dictionary.cc
+++ b/buffet/commands/command_dictionary.cc
@@ -5,10 +5,10 @@
 #include "buffet/commands/command_dictionary.h"
 
 #include <base/values.h>
+#include <chromeos/string_utils.h>
 
 #include "buffet/commands/command_definition.h"
 #include "buffet/commands/schema_constants.h"
-#include "buffet/string_utils.h"
 
 namespace buffet {
 
@@ -63,8 +63,8 @@
         return false;
       }
       // Construct the compound command name as "pkg_name.cmd_name".
-      std::string full_command_name = string_utils::Join('.', package_name,
-                                                         command_name);
+      std::string full_command_name = chromeos::string_utils::Join(
+          '.', package_name, command_name);
       // Get the "parameters" definition of the command and read it into
       // an object schema.
       const base::DictionaryValue* command_schema_def = nullptr;
@@ -158,7 +158,7 @@
       dict.reset();
       return dict;
     }
-    auto cmd_name_parts = string_utils::SplitAtFirst(pair.first, '.');
+    auto cmd_name_parts = chromeos::string_utils::SplitAtFirst(pair.first, '.');
     std::string package_name = cmd_name_parts.first;
     std::string command_name = cmd_name_parts.second;
     base::DictionaryValue* package = nullptr;