Added Web Share (navigator.share) experimental web API (stub).

third_party/WebKit/Source/modules/webshare/NavigatorShare.idl

Index: third_party/WebKit/Source/modules/webshare/NavigatorShare.idl
diff --git a/third_party/WebKit/Source/modules/webshare/NavigatorShare.idl b/third_party/WebKit/Source/modules/webshare/NavigatorShare.idl
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+++ b/third_party/WebKit/Source/modules/webshare/NavigatorShare.idl
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+// 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.
+
+// https://github.com/WICG/web-share/blob/master/docs/interface.md
+
+[
+  RuntimeEnabled=WebShare,
+] partial interface Navigator {
+  // TODO(mgiuca): Take a ShareData object, not just these two fields (see
+  // spec).
+  [CallWith=ScriptState] Promise<void> share (
+    DOMString title,
+    DOMString text
+  );
+
+  // TODO(mgiuca): Add canShare method (see spec).
+};