Some improvements for Kotlin (#333)

Address review comments from magiepooh https://github.com/google/flexbox-layout/pull/329
after the original PR is merged.

demo-playground/src/main/java/com/google/android/flexbox/FlexItemClickListener.kt

@@ -26,12 +26,10 @@ import android.view.View
 internal class FlexItemClickListener(private val activity: AppCompatActivity, private val flexItemChangedListener: FlexItemChangedListener,
                                      private val viewIndex: Int) : View.OnClickListener {
 
-    override fun onClick(v: View) {
-        val fragment = FlexItemEditFragment
-                .newInstance(v.layoutParams as FlexItem, viewIndex)
-        fragment.setFlexItemChangedListener(flexItemChangedListener)
-        fragment.show(activity.supportFragmentManager, EDIT_DIALOG_TAG)
-    }
+    override fun onClick(v: View) =
+            FlexItemEditFragment.newInstance(v.layoutParams as FlexItem, viewIndex).apply {
+                setFlexItemChangedListener(flexItemChangedListener)
+            }.show(activity.supportFragmentManager, EDIT_DIALOG_TAG)
 
     companion object {
 

demo-playground/src/main/java/com/google/android/flexbox/FlexItemEditFragment.kt

@@ -374,13 +374,11 @@ internal class FlexItemEditFragment : DialogFragment() {
 
         private const val VIEW_INDEX_KEY = "view_index"
 
-        fun newInstance(flexItem: FlexItem, viewIndex: Int): FlexItemEditFragment {
-            val fragment = FlexItemEditFragment()
-            val args = Bundle()
-            args.putParcelable(FLEX_ITEM_KEY, flexItem)
-            args.putInt(VIEW_INDEX_KEY, viewIndex)
-            fragment.arguments = args
-            return fragment
+        fun newInstance(flexItem: FlexItem, viewIndex: Int) = FlexItemEditFragment().apply {
+            arguments = Bundle().apply {
+                putParcelable(FLEX_ITEM_KEY, flexItem)
+                putInt(VIEW_INDEX_KEY, viewIndex)
+            }
         }
     }
 }