Clear the calculator display when clearing the history.

Fixes b/5186736 Calculated history is not cleared if user click on clear history in menu option.

Change-Id: Ib1f1ae4fcb87db9561fafda937d860031ba5bea4

src/com/android/calculator2/Calculator.java

@@ -211,6 +211,7 @@ public class Calculator extends Activity implements PanelSwitcher.Listener, Logi
         switch (item.getItemId()) {
             case R.id.clear_history:
                 mHistory.clear();
+                mLogic.onClear();
                 break;
 
             case R.id.basic: