Fix facebook#5599: toast doesn't disappear after app exited.

Summary:Run `Toast.makeText` other than UI Thread will cause bug facebook#5599 : toast doesn't disappear after app exited.

use `UiThreadUtil.runOnUiThread` to fix this.
Closes facebook#6443

Differential Revision: D3047261

fb-gh-sync-id: 0096879f2a4b4d76bda996a32089f068ae68e3f3
shipit-source-id: 0096879f2a4b4d76bda996a32089f068ae68e3f3

ReactAndroid/src/main/java/com/facebook/react/modules/toast/ToastModule.java

@@ -17,6 +17,7 @@
 import com.facebook.react.bridge.ReactContextBaseJavaModule;
 import com.facebook.react.bridge.ReactMethod;
 import com.facebook.react.common.MapBuilder;
+import com.facebook.react.bridge.UiThreadUtil;
 
 import java.util.Map;
 
@@ -46,7 +47,12 @@ public Map<String, Object> getConstants() {
   }
 
   @ReactMethod
-  public void show(String message, int duration) {
-    Toast.makeText(getReactApplicationContext(), message, duration).show();
+  public void show(final String message, final int duration) {
+    UiThreadUtil.runOnUiThread(new Runnable() {
+      @Override
+      public void run(){
+        Toast.makeText(getReactApplicationContext(), message, duration).show();        
+      }
+    });
   }
 }