update_engine: Move glib related utils to glib_utils.h.

This patch move the remaining glib.h functions used from utils.h to
glib_utils.h.

BUG=chromium:499886
TEST=emerge-link update_engine

Change-Id: Ia727cf3d4ee29fb33fa4db500ca83ea37d23a335
Reviewed-on: https://chromium-review.googlesource.com/281446
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
Trybot-Ready: Alex Deymo <deymo@chromium.org>
diff --git a/p2p_manager.cc b/p2p_manager.cc
index 8d519fa..c1a2738 100644
--- a/p2p_manager.cc
+++ b/p2p_manager.cc
@@ -245,7 +245,7 @@
   may_be_running_ = true;  // Unless successful, we must be conservative.
 
   vector<string> args = configuration_->GetInitctlArgs(should_be_running);
-  unique_ptr<gchar*, GLibStrvFreeDeleter> argv(
+  unique_ptr<gchar*, utils::GLibStrvFreeDeleter> argv(
       utils::StringVectorToGStrv(args));
   if (!g_spawn_sync(nullptr,  // working_directory
                     argv.get(),
@@ -260,7 +260,8 @@
                << ": " << utils::GetAndFreeGError(&error);
     return false;
   }
-  unique_ptr<gchar, GLibFreeDeleter> standard_error_deleter(standard_error);
+  unique_ptr<gchar, utils::GLibFreeDeleter> standard_error_deleter(
+      standard_error);
 
   if (!WIFEXITED(exit_status)) {
     LOG(ERROR) << "Error spawning '" << utils::StringVectorToString(args)