libchromeos: Replace char with std::string in string_utils API

std::string version of functions is enough to cover char use cases.
C library was replaced with STL in Split and SplitAtFirst implementations.
Added support of splitting by empty string. Uses but reasonable implementation
is simple.

BUG=none
TEST=unittests

Change-Id: I0778722d31a7b06eea2227b4d94991ab194195cb
Reviewed-on: https://chromium-review.googlesource.com/258640
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>

buffet/commands/command_dictionary.cc

diff --git a/buffet/commands/command_dictionary.cc b/buffet/commands/command_dictionary.cc
index 1dd0407..14bead8 100644
--- a/buffet/commands/command_dictionary.cc
+++ b/buffet/commands/command_dictionary.cc
@@ -64,8 +64,8 @@
         return false;
       }
       // Construct the compound command name as "pkg_name.cmd_name".
-      std::string full_command_name = chromeos::string_utils::Join(
-          '.', package_name, command_name);
+      std::string full_command_name =
+          chromeos::string_utils::Join(".", package_name, command_name);
 
       const ObjectSchema* base_parameters_def = nullptr;
       const ObjectSchema* base_results_def = nullptr;
@@ -186,7 +186,7 @@
       dict.reset();
       return dict;
     }
-    auto cmd_name_parts = chromeos::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;

buffet/commands/command_queue_unittest.cc

diff --git a/buffet/commands/command_queue_unittest.cc b/buffet/commands/command_queue_unittest.cc
index 97431b8..12c5500 100644
--- a/buffet/commands/command_queue_unittest.cc
+++ b/buffet/commands/command_queue_unittest.cc
@@ -52,7 +52,7 @@
   // command queue.
   std::string GetIDs() const {
     using chromeos::string_utils::Join;
-    return Join(',', std::vector<std::string>(ids_.begin(), ids_.end()));
+    return Join(",", std::vector<std::string>(ids_.begin(), ids_.end()));
   }
 
  private:
@@ -107,7 +107,7 @@
   queue.Add(CreateDummyCommandInstance("base.reboot", id2));
   std::set<std::string> ids{id1, id2};  // Make sure they are sorted properly.
   std::string expected_set = chromeos::string_utils::Join(
-      ',', std::vector<std::string>(ids.begin(), ids.end()));
+      ",", std::vector<std::string>(ids.begin(), ids.end()));
   EXPECT_EQ(expected_set, dispatch.GetIDs());
   queue.Remove(id1);
   EXPECT_EQ(id2, dispatch.GetIDs());

buffet/commands/prop_constraints.cc

diff --git a/buffet/commands/prop_constraints.cc b/buffet/commands/prop_constraints.cc
index 641d0f6..ff01e05 100644
--- a/buffet/commands/prop_constraints.cc
+++ b/buffet/commands/prop_constraints.cc
@@ -37,12 +37,11 @@
 bool Constraint::ReportErrorNotOneOf(chromeos::ErrorPtr* error,
                                      const std::string& val,
                                      const std::vector<std::string>& values) {
-  chromeos::Error::AddToPrintf(error, FROM_HERE, errors::commands::kDomain,
-                               errors::commands::kOutOfRange,
-                               "Value %s is invalid. Expected one of [%s]",
-                               val.c_str(),
-                               chromeos::string_utils::Join(',',
-                                                            values).c_str());
+  chromeos::Error::AddToPrintf(
+      error, FROM_HERE, errors::commands::kDomain,
+      errors::commands::kOutOfRange,
+      "Value %s is invalid. Expected one of [%s]", val.c_str(),
+      chromeos::string_utils::Join(",", values).c_str());
   return false;
 }
 

buffet/device_registration_info.cc

diff --git a/buffet/device_registration_info.cc b/buffet/device_registration_info.cc
index ff4df89..78b72a5 100644
--- a/buffet/device_registration_info.cc
+++ b/buffet/device_registration_info.cc
@@ -65,7 +65,7 @@
     const std::string& access_token_type,
     const std::string& access_token) {
   std::string authorization =
-      chromeos::string_utils::Join(' ', access_token_type, access_token);
+      chromeos::string_utils::Join(" ", access_token_type, access_token);
   return {chromeos::http::request_header::kAuthorization, authorization};
 }
 

buffet/states/state_manager.cc

diff --git a/buffet/states/state_manager.cc b/buffet/states/state_manager.cc
index d98015d..827cd7f 100644
--- a/buffet/states/state_manager.cc
+++ b/buffet/states/state_manager.cc
@@ -111,7 +111,7 @@
   std::string package_name;
   std::string property_name;
   bool split = chromeos::string_utils::SplitAtFirst(
-      full_property_name, '.', &package_name, &property_name);
+      full_property_name, ".", &package_name, &property_name);
   if (full_property_name.empty() || (split && property_name.empty())) {
     chromeos::Error::AddTo(error, FROM_HERE, errors::state::kDomain,
                            errors::state::kPropertyNameMissing,