Implement PrintBrowser functionality.

chrome/renderer/printing/chrome_print_web_view_helper_delegate.cc

 // Copyright 2015 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 "chrome/renderer/printing/chrome_print_web_view_helper_delegate.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/strings/string_util.h"
@@ skipping 33 matching lines @@
 #if BUILDFLAG(ENABLE_EXTENSIONS)
   GURL url = frame->document().url();
   bool inside_print_preview = url.GetOrigin() == chrome::kChromeUIPrintURL;
   bool inside_pdf_extension =
       url.SchemeIs(extensions::kExtensionScheme) &&
       url.host_piece() == extension_misc::kPdfExtensionId;
   if (inside_print_preview || inside_pdf_extension) {
     // <object> with id="plugin" is created in
     // chrome/browser/resources/pdf/pdf.js.
     auto plugin_element = frame->document().getElementById("plugin");
     if (!plugin_element.isNull()) {

[skau, 2016/12/16 18:32:50]

Why is there a situation where this is null now?

       return plugin_element;
     }
-    NOTREACHED();
   }
 #endif  // BUILDFLAG(ENABLE_EXTENSIONS)
   return blink::WebElement();
 }
 
 bool ChromePrintWebViewHelperDelegate::IsPrintPreviewEnabled() {
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   return !command_line->HasSwitch(switches::kDisablePrintPreview);
 }
 
@@ skipping 12 matching lines @@
     // PDF plugin document correctly print the PDF. See
     // https://crbug.com/448720.
     base::DictionaryValue message;
     message.SetString("type", "print");
     mime_handlers.front()->PostMessageFromValue(message);
     return true;
   }
 #endif  // BUILDFLAG(ENABLE_EXTENSIONS)
   return false;
 }