Make RunApplication() return a MojoResult and TerminateApplication() take one.

mojo/public/cpp/application/run_application.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_APPLICATION_RUN_APPLICATION_H_
 #define MOJO_PUBLIC_CPP_APPLICATION_RUN_APPLICATION_H_
 
 #include "mojo/public/c/system/handle.h"
 #include "mojo/public/c/system/result.h"
 
 namespace mojo {
 
 class ApplicationImplBase;
 
 // Sets up a message (run) loop and runs the provided application
-// implementation.
+// implementation. The return value will be the one provided to
+// |TerminateApplication()|.
 //
 // Typical use (where |MyApplicationImpl| is an implementation of
 // |ApplicationImplBase|):
 //
 //   MojoResult MojoMain(MojoHandle application_request_handle) {
 //     MyApplicationImpl my_app;
-//     mojo::RunApplication(application_request_handle, &my_app);
-//     return MOJO_RESULT_OK;
+//     return mojo::RunApplication(application_request_handle, &my_app);
 //   }
 //
 // Note that this may actually be used on any thread (that is not already
 // running a message loop of some sort).
 //
 // |*application_impl| must remain alive until the message loop starts running
 // (thus it may own itself).
 //
-// TODO(vtl): Possibly this should return a |MojoResult| and
-// |TerminateApplication()| should take a |MojoResult| argument (which this
-// returns), but to communicate that value requires TLS.
 // TODO(vtl): Maybe this should be like |Environment|, with different possible
 // implementations (e.g., "standalone" vs "chromium"). However,
 // |ApplicationRunnerChromium| currently has additional goop specific to the
-// main thread. Probably we should have additional "MainRunApplication()" and
-// "MainTerminateApplication()" functions.
-void RunApplication(MojoHandle application_request_handle,
-                    ApplicationImplBase* application_impl);
+// main thread. Probably we should have additional "RunMainApplication()" and
+// "TerminateMainApplication()" functions.
+MojoResult RunApplication(MojoHandle application_request_handle,
+                          ApplicationImplBase* application_impl);
 
 // Terminates the currently-running application. This may only be called from
 // "inside" |RunApplication()| (i.e., it is on the stack, which means that the
 // message loop is running). This will cause |RunApplication()| to return "soon"
-// (assuming the message loop is not blocked processing some task). This may
-// cause queued work to *not* be executed.
-void TerminateApplication();
+// (assuming the message loop is not blocked processing some task), with return
+// value |result|. This may cause queued work to *not* be executed. This should
+// be executed at most once (per |RunApplication()|).
+void TerminateApplication(MojoResult result);
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_APPLICATION_RUN_APPLICATION_H_