[Reland] Refactor WebappRegistry into a singleton instance.

chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java

Index: chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java b/chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java
index 4ebeee589ab90ad1b4bd056bbbd9baf5e70c9cec..36a231ea5b3f2f2090ab581c4ff71205af5d1c6c 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/DeferredStartupHandler.java
@@ -48,6 +48,7 @@ import org.chromium.chrome.browser.preferences.privacy.PrivacyPreferencesManager
 import org.chromium.chrome.browser.share.ShareHelper;
 import org.chromium.chrome.browser.webapps.ChromeWebApkHost;
 import org.chromium.chrome.browser.webapps.WebApkVersionManager;
+import org.chromium.chrome.browser.webapps.WebappRegistry;
 import org.chromium.content.browser.ChildProcessLauncher;
 
 import java.util.ArrayList;
@@ -278,11 +279,20 @@ public class DeferredStartupHandler {
                             SystemClock.uptimeMillis() - asyncTaskStartTime,
                             TimeUnit.MILLISECONDS);
 
+                    // Warm up all web app shared prefs.
+                    WebappRegistry.warmUpSharedPrefs("");
+
                     return null;
                 } finally {
                     TraceEvent.end("ChromeBrowserInitializer.onDeferredStartup.doInBackground");
                 }
             }
+
+            @Override
+            protected void onPostExecute(Void params) {
+                // Must be run on the UI thread after the WebappRegistry has been completely warmed.
+                WebappRegistry.getInstance().unregisterOldWebapps(System.currentTimeMillis());
+            }
         }.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
     }