Migrate files to embedder.

samples/android_sample/jni/main.cc

-#include "jni/context.h"
-#include "jni/dart_host.h"
-#include "jni/eventloop.h"
-#include "jni/graphics.h"
-#include "jni/input_service.h"
-#include "jni/vm_glue.h"
-
-SoundService* psound_service;
-
-void android_main(android_app* application) {
-  Timer timer;
-  Graphics graphics(application, &timer);
-  VMGlue vmGlue(&graphics);
-  InputService inputService(application, &vmGlue,
-      graphics.width(), graphics.height());
-  SoundService sound_service(application);
-  psound_service = &sound_service;
-  Context context;
-  context = { &graphics, &inputService, psound_service, &timer, &vmGlue };
-  EventLoop eventLoop(application);
-  DartHost host(&context);
-  eventLoop.Run(&host, &context);
-}
-
-void PlayBackground(const char* path) {
-  psound_service->PlayBackground(path);
-}
-
-void StopBackground() {
-  psound_service->StopBackground();
-}