Add DownloadPDF Callback function.

chrome/renderer/plugins/pdf_plugin_placeholder.cc

Index: chrome/renderer/plugins/pdf_plugin_placeholder.cc
diff --git a/chrome/renderer/plugins/pdf_plugin_placeholder.cc b/chrome/renderer/plugins/pdf_plugin_placeholder.cc
index 3263551c8f9bbf9fb0f54b346856ffb04d9ffba5..6e20cfbce38d5d95d2839659ae16a40719d2095a 100644
--- a/chrome/renderer/plugins/pdf_plugin_placeholder.cc
+++ b/chrome/renderer/plugins/pdf_plugin_placeholder.cc
@@ -5,6 +5,7 @@
 #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"
 
@@ -31,3 +32,14 @@ PDFPluginPlaceholder* PDFPluginPlaceholder::CreatePDFPlaceholder(
 v8::Local<v8::Value> PDFPluginPlaceholder::GetV8Handle(v8::Isolate* isolate) {
   return gin::CreateHandle(isolate, this).ToV8();
 }
+
+gin::ObjectTemplateBuilder PDFPluginPlaceholder::GetObjectTemplateBuilder(
+    v8::Isolate* isolate) {
+  return gin::Wrappable<PDFPluginPlaceholder>::GetObjectTemplateBuilder(isolate)
+      .SetMethod<void (PDFPluginPlaceholder::*)()>(
+          "downloadPDF", &PDFPluginPlaceholder::DownloadPDFCallback);
+}
+
+void PDFPluginPlaceholder::DownloadPDFCallback() {
+  // TODO(amberwon): Implement starting PDF download.
+}