Keep Keyboard object while closing KeyboardView

Bug: 8217626
Change-Id: Ie00ba827bc391aa152427965c57488b66308a75c
diff --git a/java/src/com/android/inputmethod/keyboard/KeyboardView.java b/java/src/com/android/inputmethod/keyboard/KeyboardView.java
index 4dab50f..365c35b 100644
--- a/java/src/com/android/inputmethod/keyboard/KeyboardView.java
+++ b/java/src/com/android/inputmethod/keyboard/KeyboardView.java
@@ -635,9 +635,9 @@
         invalidate(x, y, x + key.mWidth, y + key.mHeight);
     }
 
+    // TODO: Remove this method.
     public void closing() {
         mInvalidateAllKeys = true;
-        mKeyboard = null;
     }
 
     @Override