Add get native window interface (#209)

* Add get ecore window interface.

* Change get window method name

* Fix build error

* Fix build error

* Add comment for getting window interface

* Remove not used code

* Change interface name

1.Change interface name, make it more clearly.
2.Move HandleForRender and RendererFromHandle to unnamed namspace.

* Get window from FlutterDesktopPluginRegistrarRef

* Merge GetWindow and GetWindowHandle

Author: xiaowei-guan

shell/platform/tizen/flutter_tizen.cc

@@ -77,6 +77,10 @@ void FlutterDesktopShutdownEngine(FlutterDesktopEngineRef engine_ref) {
   delete engine;
 }
 
+void* FlutterDesktopGetWindow(FlutterDesktopPluginRegistrarRef registrar) {
+  return registrar->engine->renderer()->GetWindowHandle();
+}
+
 void FlutterDesktopPluginRegistrarEnableInputBlocking(
     FlutterDesktopPluginRegistrarRef registrar,
     const char* channel) {

shell/platform/tizen/public/flutter_tizen.h

@@ -91,6 +91,15 @@ FlutterDesktopGetPluginRegistrar(FlutterDesktopEngineRef engine,
 FLUTTER_EXPORT FlutterDesktopMessengerRef
 FlutterDesktopEngineGetMessenger(FlutterDesktopEngineRef engine);
 
+/**
+ * Return backing window for manipulation in host application.
+ *
+ * If run engine on a wearable device, need cast void* to Evas_Objct*,
+ * otherwise cast void* to Ecore_Wl2_Window*.
+ */
+FLUTTER_EXPORT void* FlutterDesktopGetWindow(
+    FlutterDesktopPluginRegistrarRef registrar);
+
 // Posts an app control to the engine instance.
 FLUTTER_EXPORT void FlutterDesktopNotifyAppControl(
     FlutterDesktopEngineRef engine,

shell/platform/tizen/tizen_renderer_evas_gl.cc

@@ -576,7 +576,7 @@ uintptr_t TizenRendererEvasGL::GetWindowId() {
 }
 
 void* TizenRendererEvasGL::GetWindowHandle() {
-  return nullptr;
+  return evas_window_;
 }
 
 Evas_Object* TizenRendererEvasGL::GetImageHandle() {