Propagate drag-and-drop key modifiers to WebView's guest renderer.

content/public/common/drop_data.cc

 // Copyright 2013 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/public/common/drop_data.h"
 
 namespace content {
 
 DropData::DropData()
     : did_originate_from_renderer(false),
-      referrer_policy(blink::WebReferrerPolicyDefault) {}
+      referrer_policy(blink::WebReferrerPolicyDefault),
+      key_modifiers(0) {}
 
 DropData::DropData(const DropData& other) = default;
 
 DropData::~DropData() {
 }
 
 }  // namespace content