Add a mojo::RunApplication() for running implementations of ApplicationImplBase.

mojo/public/cpp/application/BUILD.gn

Index: mojo/public/cpp/application/BUILD.gn
diff --git a/mojo/public/cpp/application/BUILD.gn b/mojo/public/cpp/application/BUILD.gn
index ec0deae3984fb215449281d8c4802a9ec93d882b..d46f34aa807e2582b451d9519ac0ef5e02ee5dca 100644
--- a/mojo/public/cpp/application/BUILD.gn
+++ b/mojo/public/cpp/application/BUILD.gn
@@ -32,7 +32,10 @@ mojo_sdk_source_set("application") {
 # GYP version: mojo/public/mojo_public.gyp:mojo_application_standalone
 mojo_sdk_source_set("standalone") {
   sources = [
+    "application_runner.h",
     "lib/application_runner.cc",
+    "lib/run_application.cc",
+    "run_application.h",
   ]
 
   public_deps = [
@@ -41,7 +44,9 @@ mojo_sdk_source_set("standalone") {
 
   mojo_sdk_deps = [
     "mojo/public/cpp/environment:standalone",
+    "mojo/public/cpp/system",
     "mojo/public/cpp/utility",
+    "mojo/public/interfaces/application",
   ]
 }