Add DownloadPDF Callback function.

chrome/renderer/plugins/pdf_plugin_placeholder.cc

 // Copyright 2017 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/plugins/pdf_plugin_placeholder.h"
 
 #include "chrome/grit/renderer_resources.h"
+#include "gin/object_template_builder.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/base/webui/jstemplate_builder.h"
 
 gin::WrapperInfo PDFPluginPlaceholder::kWrapperInfo = {gin::kEmbedderNativeGin};
 
 PDFPluginPlaceholder::PDFPluginPlaceholder(content::RenderFrame* render_frame,
                                            const blink::WebPluginParams& params,
                                            const std::string& html_data)
     : plugins::PluginPlaceholderBase(render_frame, params, html_data) {}
 
 PDFPluginPlaceholder::~PDFPluginPlaceholder() {}
 
 PDFPluginPlaceholder* PDFPluginPlaceholder::CreatePDFPlaceholder(
     content::RenderFrame* render_frame,
     const blink::WebPluginParams& params) {
   const base::StringPiece template_html(
       ResourceBundle::GetSharedInstance().GetRawDataResource(
           IDR_PDF_PLUGIN_HTML));
   base::DictionaryValue values;
   std::string html_data = webui::GetI18nTemplateHtml(template_html, &values);
   return new PDFPluginPlaceholder(render_frame, params, html_data);
 }
 
 v8::Local<v8::Value> PDFPluginPlaceholder::GetV8Handle(v8::Isolate* isolate) {
   return gin::CreateHandle(isolate, this).ToV8();
 }
+
+gin::ObjectTemplateBuilder PDFPluginPlaceholder::GetObjectTemplateBuilder(
+    v8::Isolate* isolate) {
+  gin::ObjectTemplateBuilder builder =
+      gin::Wrappable<PDFPluginPlaceholder>::GetObjectTemplateBuilder(isolate)
+          .SetMethod<void (PDFPluginPlaceholder::*)()>(
+              "downloadPDF", &PDFPluginPlaceholder::DownloadPDFCallback);
+
+  return builder;

[tommycli, 2017/07/05 19:46:23]

I think you can just return it directly like here:
https://cs.chromium.org/chromium/src/components/plugins/renderer/plugin_place...

[amberwon, 2017/07/05 19:54:02]

Done.

+}
+
+void PDFPluginPlaceholder::DownloadPDFCallback() {
+  // TODO(amberwon): Download PDF.

[tommycli, 2017/07/05 19:46:23]

TODO(amberwon): Implement starting PDF download.

[amberwon, 2017/07/05 19:54:02]

Done.

+}