Fix broken KeyguardMessageArea

Fixes a bug where the keyguard message area would reorder clears
after a new message was set, leading to the bouncer prompt reason
not showing.

Change-Id: I33001300d9175c521809cd4fdae5158269245c00
Fixes: 32306174
Test: runtest -x $T/frameworks/base/packages/SystemUI/tests/src/com/android/keyguard/KeyguardMessageAreaTest.java

packages/SystemUI/tests/src/com/android/keyguard/KeyguardMessageAreaTest.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+package com.android.keyguard;
+
+import com.android.systemui.SysuiTestCase;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import android.content.Context;
+import android.os.Handler;
+import android.os.Looper;
+import android.support.test.InstrumentationRegistry;
+import android.support.test.runner.AndroidJUnit4;
+import android.test.suitebuilder.annotation.SmallTest;
+
+import static junit.framework.Assert.*;
+import static org.mockito.Mockito.mock;
+
+@SmallTest
+@RunWith(AndroidJUnit4.class)
+public class KeyguardMessageAreaTest extends SysuiTestCase {
+    private Context mContext = InstrumentationRegistry.getTargetContext();
+    private Handler mHandler = new Handler(Looper.getMainLooper());
+    private KeyguardMessageArea mMessageArea;
+
+    @Before
+    public void setUp() throws Exception {
+        KeyguardUpdateMonitor monitor = mock(KeyguardUpdateMonitor.class);
+        mHandler.post(()-> mMessageArea = new KeyguardMessageArea(mContext, null, monitor));
+        waitForIdleSync();
+    }
+
+    @Test
+    public void clearFollowedByMessage_keepsMessage() {
+        mHandler.post(()-> {
+            mMessageArea.setMessage("");
+            mMessageArea.setMessage("test");
+        });
+
+        waitForIdleSync();
+
+        CharSequence[] messageText = new CharSequence[1];
+        mHandler.post(()-> {
+            messageText[0] = mMessageArea.getText();
+        });
+
+        waitForIdleSync();
+
+        assertEquals("test", messageText[0]);
+    }
+
+}