Store URLs in WebappDataStorage, and purge them when history is cleared.

chrome/browser/android/webapps/webapp_registry.h

 // Copyright 2015 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.
 
 #ifndef CHROME_BROWSER_ANDROID_WEBAPPS_WEBAPP_REGISTRY_H_
 #define CHROME_BROWSER_ANDROID_WEBAPPS_WEBAPP_REGISTRY_H_
 
 #include "base/android/jni_android.h"
 #include "base/android/scoped_java_ref.h"
 #include "base/callback_forward.h"
 #include "base/macros.h"
 
 // WebappRegistry is the C++ counterpart of
 // org.chromium.chrome.browser.webapp's WebappRegistry in Java.
 class WebappRegistry {
  public:
   // Registers JNI hooks.
   static bool RegisterWebappRegistry(JNIEnv* env);
 
   // Cleans up data stored by web apps.
   static void UnregisterWebapps(const base::Closure& callback);
 
+  // Removes history data (last used time and URLs) stored by web apps, whilst
+  // leaving other data intact.
+  static void ClearWebappHistory(const base::Closure& callback);
+
  private:
   ~WebappRegistry() = delete;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(WebappRegistry);
 };
 
 #endif  // CHROME_BROWSER_ANDROID_WEBAPPS_WEBAPP_REGISTRY_H_