Listen to didReceiveResponse() to get the response in WebViewPlugin.

components/plugins/renderer/webview_plugin.h

 // 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.
 
 #ifndef COMPONENTS_PLUGINS_RENDERER_WEBVIEW_PLUGIN_H_
 #define COMPONENTS_PLUGINS_RENDERER_WEBVIEW_PLUGIN_H_
 
 #include <list>
 #include <memory>
 
@@ skipping 90 matching lines @@
                       const blink::WebVector<blink::WebRect>& cut_outs_rects,
                       bool is_visible) override;
 
   void updateFocus(bool foucsed, blink::WebFocusType focus_type) override;
   void updateVisibility(bool) override {}
 
   blink::WebInputEventResult handleInputEvent(
       const blink::WebInputEvent& event,
       blink::WebCursorInfo& cursor_info) override;
 
-  void didReceiveResponse(const blink::WebURLResponse& response) override {}
+  void didReceiveResponse(const blink::WebURLResponse& response) override;
   void didReceiveData(const char* data, int data_length) override;
   void didFinishLoading() override;
   void didFailLoading(const blink::WebURLError& error) override;
 
   // WebViewClient methods:
   bool acceptsLoadDrops() override;
 
   void setToolTipText(const blink::WebString&,
                       blink::WebTextDirection) override;
 
@@ skipping 40 matching lines @@
   // Owned by us, deleted via |close()|.
   blink::WebView* web_view_;
 
   // Owned by us, deleted via |close()|.
   blink::WebFrameWidget* web_frame_widget_;
 
   // Owned by us, deleted via |close()|.
   blink::WebFrame* web_frame_;
   gfx::Rect rect_;
 
+  blink::WebURLResponse response_;
   std::list<std::string> data_;
   std::unique_ptr<blink::WebURLError> error_;
   blink::WebString old_title_;
   bool finished_loading_;
   bool focused_;
   bool is_painting_;
   bool is_resizing_;
 
   // Should be invalidated when destroy() is called.
   base::WeakPtrFactory<WebViewPlugin> weak_factory_;
 };
 
 #endif  // COMPONENTS_PLUGINS_RENDERER_WEBVIEW_PLUGIN_H_