Implemented stub ShareService mojo service, for navigator.share.

content/browser/webshare/share_service_impl.cc

+// 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.
+
+#include "content/browser/webshare/share_service_impl.h"
+
+#include "mojo/public/cpp/bindings/strong_binding.h"
+
+// static
+void ShareServiceImpl::Create(blink::mojom::ShareServiceRequest request) {
+  mojo::MakeStrongBinding(base::MakeUnique<ShareServiceImpl>(),
+                          std::move(request));
+}
+
+void ShareServiceImpl::Share(const std::string& title,
+                             const std::string& text,
+                             const GURL& url,
+                             const ShareCallback& callback) {
+  // TODO(constantina): Implement Web Share Target here.
+  NOTIMPLEMENTED();
+  callback.Run(base::Optional<std::string>("Not implemented: navigator.share"));
+}