Refactored Android samples / 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);
 }
 
-int32_t PlayBackground(const char* path) {
+void PlayBackground(const char* path) {
   psound_service->PlayBackground(path);
 }
 
 void StopBackground() {
   psound_service->StopBackground();
 }
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