[Reland] Refactor WebappRegistry into a singleton instance.

chrome/android/javatests/src/org/chromium/chrome/browser/webapps/TestFetchStorageCallback.java

Index: chrome/android/javatests/src/org/chromium/chrome/browser/webapps/TestFetchStorageCallback.java
diff --git a/chrome/android/javatests/src/org/chromium/chrome/browser/webapps/TestFetchStorageCallback.java b/chrome/android/javatests/src/org/chromium/chrome/browser/webapps/TestFetchStorageCallback.java
new file mode 100644
index 0000000000000000000000000000000000000000..567fb537f47e6662bae7dc8176e0e97d588f716f
--- /dev/null
+++ b/chrome/android/javatests/src/org/chromium/chrome/browser/webapps/TestFetchStorageCallback.java
@@ -0,0 +1,25 @@
+// 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 org.chromium.content.browser.test.util.CallbackHelper;
+
+/**
+ * CallbackHelper subclass which implements WebappRegistry.FetchWebappDataStorageCallback for tests.
+ */
+public class TestFetchStorageCallback
+        extends CallbackHelper implements WebappRegistry.FetchWebappDataStorageCallback {
+    protected WebappDataStorage mStorage;
+
+    @Override
+    public void onWebappDataStorageRetrieved(WebappDataStorage storage) {
+        mStorage = storage;
+        notifyCalled();
+    }
+
+    public WebappDataStorage getStorage() {
+        return mStorage;
+    }
+}