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>

utils.cc

diff --git a/utils.cc b/utils.cc
index 03f642a..f36cbec 100644
--- a/utils.cc
+++ b/utils.cc
@@ -40,7 +40,6 @@
 #include <chromeos/data_encoding.h>
 #include <chromeos/key_value_store.h>
 #include <chromeos/message_loops/message_loop.h>
-#include <glib.h>
 
 #include "update_engine/clock_interface.h"
 #include "update_engine/constants.h"
@@ -676,7 +675,7 @@
 
     TEST_AND_RETURN_FALSE_ERRNO(errno == EBUSY &&
                                 num_retries < kUnmountMaxNumOfRetries);
-    g_usleep(kUnmountRetryIntervalInMicroseconds);
+    usleep(kUnmountRetryIntervalInMicroseconds);
   }
   return true;
 }
@@ -1503,15 +1502,6 @@
   return Time::UnixEpoch() + TimeDelta::FromMicroseconds(us);
 }
 
-gchar** StringVectorToGStrv(const vector<string> &vec_str) {
-  GPtrArray *p = g_ptr_array_new();
-  for (const string& str : vec_str) {
-    g_ptr_array_add(p, g_strdup(str.c_str()));
-  }
-  g_ptr_array_add(p, nullptr);
-  return reinterpret_cast<gchar**>(g_ptr_array_free(p, FALSE));
-}
-
 string StringVectorToString(const vector<string> &vec_str) {
   string str = "[";
   for (vector<string>::const_iterator i = vec_str.begin();