[Android Refactor] Reland: Merge WebappDataStorage#LAST_USED_UNSET and LAST_USED_INVALID

chrome/android/junit/src/org/chromium/chrome/browser/webapps/WebApkUpdateManagerTest.java

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.webapps;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
@@ skipping 53 matching lines @@
     private static final int DISPLAY_MODE = WebDisplayMode.UNDEFINED;
     private static final int ORIENTATION = ScreenOrientationValues.DEFAULT;
     private static final long THEME_COLOR = 1L;
     private static final long BACKGROUND_COLOR = 2L;
 
     /** Different name than the one used in {@link defaultManifestData()}. */
     private static final String DIFFERENT_NAME = "Different Name";
 
     /** {@link WebappDataStorage#Clock} subclass which enables time to be manually advanced. */
     private static class MockClock extends WebappDataStorage.Clock {
-        // 0 has a special meaning: {@link WebappDataStorage#LAST_USED_UNSET}.
+        // 0 has a special meaning: {@link WebappDataStorage#TIMESTAMP_INVALID}.
         private long mTimeMillis = 1;
 
         public void advance(long millis) {
             mTimeMillis += millis;
         }
 
         @Override
         public long currentTimeMillis() {
             return mTimeMillis;
         }
@@ skipping 696 matching lines @@
 
         // A previous update request was made for the current ShellAPK version. A WebAPK update
         // should be requested after the regular delay.
         mClock.advance(WebappDataStorage.UPDATE_INTERVAL - 1);
         updateIfNeeded(updateManager);
         assertTrue(updateManager.updateCheckStarted());
         onGotManifestData(updateManager, defaultManifestData());
         assertTrue(updateManager.updateRequested());
     }
 }