When KEYCODE_BACK is received, hide keyboard

Bug: 191845409
Bug: 190351740

Test: manual
Change-Id: I9e3a55f7eb81b2c2a668532ebb991cefbf248163
diff --git a/src/com/android/launcher3/ExtendedEditText.java b/src/com/android/launcher3/ExtendedEditText.java
index e8510b7..a4e1af6 100644
--- a/src/com/android/launcher3/ExtendedEditText.java
+++ b/src/com/android/launcher3/ExtendedEditText.java
@@ -70,6 +70,9 @@
     public boolean onKeyPreIme(int keyCode, KeyEvent event) {
         // If this is a back key, propagate the key back to the listener
         if (keyCode == KeyEvent.KEYCODE_BACK && event.getAction() == KeyEvent.ACTION_UP) {
+            if (TextUtils.isEmpty(getText())) {
+                hideKeyboard();
+            }
             if (mBackKeyListener != null) {
                 return mBackKeyListener.onBackKey();
             }