Adds support for mojo apps to live in their own directory

mojo/runner/BUILD.gn

Index: mojo/runner/BUILD.gn
diff --git a/mojo/runner/BUILD.gn b/mojo/runner/BUILD.gn
index d9ddc78485ca9fae10559c60cf3768aa11e175d5..4028b1ce0be443327ad5da862dc2e6fe7b297a80 100644
--- a/mojo/runner/BUILD.gn
+++ b/mojo/runner/BUILD.gn
@@ -95,8 +95,6 @@ source_set("lib") {
     "child_process_host.h",
     "context.cc",
     "context.h",
-    "filename_util.cc",
-    "filename_util.h",
     "init.cc",
     "init.h",
     "out_of_process_native_runner.cc",
@@ -117,6 +115,7 @@ source_set("lib") {
     "//mojo/application",
     "//mojo/common",
     "//mojo/common:tracing_impl",
+    "//mojo/util:filename_util",
     "//third_party/mojo/src/mojo/edk/system",
     "//third_party/mojo/src/mojo/public/cpp/bindings",
     "//third_party/mojo/src/mojo/public/interfaces/application",
@@ -355,14 +354,15 @@ test("tests") {
     "//base",
     "//base:i18n",
     "//base/test:test_support",
-    "//testing/gtest",
-    "//url",
     "//mojo/common",
-    "//third_party/mojo/src/mojo/edk/system",
     "//mojo/environment:chromium",
-    "//third_party/mojo/src/mojo/public/cpp/bindings",
     "//mojo/services/test_service:bindings",
     "//mojo/shell",
+    "//mojo/util:filename_util",
+    "//testing/gtest",
+    "//third_party/mojo/src/mojo/edk/system",
+    "//third_party/mojo/src/mojo/public/cpp/bindings",
+    "//url",
   ]
 
   datadeps = [