Show a new placeholder for PDF's when plugins are disabled.

chrome/renderer/plugins/pdf_plugin_placeholder.h

+// 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.
+
+#ifndef CHROME_RENDERER_PLUGINS_PDF_PLUGIN_PLACEHOLDER_H_
+#define CHROME_RENDERER_PLUGINS_PDF_PLUGIN_PLACEHOLDER_H_
+
+#include "components/plugins/renderer/plugin_placeholder.h"
+
+// Placeholder that allows users to click to download a PDF for when
+// plugins are disabled and the PDF fails to load.
+// TODO(amberwon): Flesh out the class more to download an embedded PDF when the
+// PDF plugin is disabled or unavailable.
+class PDFPluginPlaceholder : public plugins::PluginPlaceholderBase,
+                             public gin::Wrappable<PDFPluginPlaceholder> {
+ public:
+  static gin::WrapperInfo kWrapperInfo;
+
+  // Returned pointer is owned by plugin, which can be returned by the member

[Lei Zhang, 2017/06/30 22:45:11]

Nobody actually owns the pointer. It's the object whose lifetime is actually
important.

[amberwon, 2017/06/30 23:11:12]

Done.

+  // function plugin().

[Lei Zhang, 2017/06/30 22:45:11]

Except I don't see a plugin() function in this file, so as a reader of this
comment, it's not obvious what it is referring to. So putting it all together,
how about:

Returned placeholder is owned by the associated plugin, which can be retrieved
with PluginPlaceholderBase::plugin().

[amberwon, 2017/06/30 23:11:12]

Done.

+  static PDFPluginPlaceholder* CreatePDFPlaceholder(
+      content::RenderFrame* render_frame,
+      const blink::WebPluginParams& params);
+
+ private:
+  PDFPluginPlaceholder(content::RenderFrame* render_frame,
+                       const blink::WebPluginParams& params,
+                       const std::string& html_data);
+  ~PDFPluginPlaceholder() override;
+
+  // WebViewPlugin::Delegate methods:
+  v8::Local<v8::Value> GetV8Handle(v8::Isolate* isolate) override;
+};
+
+#endif  // CHROME_RENDERER_PLUGINS_PDF_PLUGIN_PLACEHOLDER_H_