Adds support for mojo apps to live in their own directory

mojo/util/BUILD.gn

Index: mojo/util/BUILD.gn
diff --git a/device/bluetooth/uribeacon/BUILD.gn b/mojo/util/BUILD.gn
similarity index 69%
copy from device/bluetooth/uribeacon/BUILD.gn
copy to mojo/util/BUILD.gn
index 484e27270327646f886047b1d4d39d1a2e6641f1..379bc96230e7c6037bca99a4a311de60a65c109a 100644
--- a/device/bluetooth/uribeacon/BUILD.gn
+++ b/mojo/util/BUILD.gn
@@ -2,12 +2,14 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source_set("uribeacon") {
+source_set("filename_util") {
   sources = [
-    "uri_encoder.cc",
-    "uri_encoder.h",
+    "filename_util.cc",
+    "filename_util.h",
   ]
+
   deps = [
     "//base",
+    "//url",
   ]
 }