Add a Physical Web data source

ios/chrome/browser/physical_web/create_physical_web_data_source.h

+// 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.
+
+#ifndef IOS_CHROME_BROWSER_PHYSICAL_WEB_CREATE_PHYSICAL_WEB_DATA_SOURCE_H_
+#define IOS_CHROME_BROWSER_PHYSICAL_WEB_CREATE_PHYSICAL_WEB_DATA_SOURCE_H_
+
+#include <memory>
+
+class PhysicalWebDataSource;
+
+// Creates a new instance of IOSChromePhysicalWebDataSource. The returned object
+// is fully initialized and can be registered as global singleton.
+//
+// This helper function allows the construction of

[sdefresne, 2016/08/02 22:23:36]

I would remove this paragraph as it is an implementation details that may become
obsolete someday.

[mattreynolds, 2016/08/04 00:56:12]

Done.

+// IOSChromePhysicalWebDataSource from pure C++ (IOSChromePhysicalWebDataSource
+// is an Objective-C++ class).
+std::unique_ptr<PhysicalWebDataSource> CreateIOSChromePhysicalWebDataSource();
+
+#endif  // IOS_CHROME_BROWSER_PHYSICAL_WEB_CREATE_PHYSICAL_WEB_DATA_SOURCE_H_