Refactor and cleanup codes. No functional changes.

util/gtl/BUILD

@@ -0,0 +1,19 @@
+################################################################################
+# Copyright 2017 Google LLC.
+#
+# This software is licensed under the terms defined in the Widevine Master
+# License Agreement. For a copy of this agreement, please contact
+# widevine-licensing@google.com.
+################################################################################
+
+package(
+    default_visibility = ["//visibility:public"],
+)
+
+
+cc_library(
+    name = "map_util",
+    hdrs = [
+        "map_util.h",
+    ],
+)