Move WebappRegistry warmup to async task.

On Android N the constructor results in a StrictMode violation due to
WebappRegistry#openSharedPreferences. Use initialization on demand
holder idiom to avoid synchronization issues.

BUG=656035

Review-Url: https://chromiumcodereview.appspot.com/2421833003
Cr-Commit-Position: refs/heads/master@{#426823}

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

@@ -174,10 +174,6 @@ public class DeferredStartupHandler {
         mDeferredTasks.add(new Runnable() {
             @Override
             public void run() {
-                // Initialize the WebappRegistry if it's not already initialized. Must be done on
-                // the main thread.
-                WebappRegistry.getInstance();
-
                 // Punt all tasks that may block on disk off onto a background thread.
                 initAsyncDiskTask();
 
@@ -243,6 +239,11 @@ public class DeferredStartupHandler {
                 try {
                     TraceEvent.begin("ChromeBrowserInitializer.onDeferredStartup.doInBackground");
                     long asyncTaskStartTime = SystemClock.uptimeMillis();
+
+                    // Initialize the WebappRegistry if it's not already initialized. Must be in
+                    // async task due to shared preferences disk access on N.
+                    WebappRegistry.getInstance();
+
                     boolean crashDumpDisabled = CommandLine.getInstance().hasSwitch(
                             ChromeSwitches.DISABLE_CRASH_DUMP_UPLOAD);
                     if (!crashDumpDisabled) {

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappRegistry.java

@@ -49,7 +49,11 @@ public class WebappRegistry {
     /** Represents a period of 13 weeks in milliseconds */
     static final long WEBAPP_UNOPENED_CLEANUP_DURATION = TimeUnit.DAYS.toMillis(13L * 7L);
 
-    private static volatile WebappRegistry sInstance;
+    /** Initialization-on-demand holder. This exists for thread-safe lazy initialization. */
+    private static class Holder {
+        // Not final for testing.
+        private static WebappRegistry sInstance = new WebappRegistry();
+    }
 
     private HashMap<String, WebappDataStorage> mStorages;
     private SharedPreferences mPreferences;
@@ -62,34 +66,37 @@ public class WebappRegistry {
         void onWebappDataStorageRetrieved(WebappDataStorage storage);
     }
 
+    private WebappRegistry() {
+        mPreferences = openSharedPreferences();
+        mStorages = new HashMap<>();
+    }
+
     /**
-     * Returns the singleton WebappRegistry instance. Creates the instance if necessary.
+     * Returns the singleton WebappRegistry instance. Creates the instance on first call.
      */
     public static WebappRegistry getInstance() {
-        if (sInstance == null) sInstance = new WebappRegistry();
-        return sInstance;
+        return Holder.sInstance;
     }
 
     /**
-     * Warm up the WebappRegistry and a specific WebappDataStorage SharedPreferences. This static
-     * method can be called on any thread, so it must not initialize sInstance.
+     * Warm up the WebappRegistry and a specific WebappDataStorage SharedPreferences.
      * @param id The web app id to warm up in addition to the WebappRegistry.
      */
     public static void warmUpSharedPrefsForId(String id) {
-        sInstance.initStorages(id, false);
+        getInstance().initStorages(id, false);
     }
 
     /**
-     * Warm up the WebappRegistry and all WebappDataStorage SharedPreferences. This static method
-     * can be called on any thread, so it must not initialize sInstance.
+     * Warm up the WebappRegistry and all WebappDataStorage SharedPreferences.
      */
     public static void warmUpSharedPrefs() {
-        sInstance.initStorages(null, false);
+        getInstance().initStorages(null, false);
     }
 
+    @VisibleForTesting
     public static void refreshSharedPrefsForTesting() {
-        sInstance = new WebappRegistry();
-        sInstance.initStorages(null, true);
+        Holder.sInstance = new WebappRegistry();
+        getInstance().initStorages(null, true);
     }
 
     /**
@@ -264,11 +271,6 @@ public class WebappRegistry {
                 REGISTRY_FILE_NAME, Context.MODE_PRIVATE);
     }
 
-    private WebappRegistry() {
-        mPreferences = openSharedPreferences();
-        mStorages = new HashMap<String, WebappDataStorage>();
-    }
-
     private void initStorages(String idToInitialize, boolean replaceExisting) {
         Set<String> webapps =
                 mPreferences.getStringSet(KEY_WEBAPP_SET, Collections.<String>emptySet());