Add plugin placeholder and policy support (issue #1708)

- Default plugin loading policy can be specified using the new
  `--plugin-policy=[allow|block|detect]` command-line flag.
- Move CefRequestHandler::OnBeforePluginLoad to
  CefRequestContextHandler and add a new policy argument that
  supports different actions (allow, block, detect, disable) on a
  per-plugin-instance basis.
- Add CefContextMenuHandler::RunContextMenu for providing a custom
  context menu implementation.
- Add CefResourceBundleHandler::GetDataResourceForScale for
  returning scaled resources (issue #1272).
- Add CefResourceBundle for retrieving resources from the resource
  bundle (*.pak) files loaded by CEF during startup or via the
  CefResourceBundleHandler.
- Linux: Fix Debug build IO access warning with CefGetMimeType.
- cef_unittests: Move the refcounting implementation from TestHandler
  to subclasses in order to support interface inheritance from
  subclasses.

libcef/renderer/plugins/cef_plugin_placeholder.h

@@ -0,0 +1,102 @@
+// 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 CEF_LIBCEF_RENDERER_PLUGINS_CEF_PLUGIN_PLACEHOLDER_H_
+#define CEF_LIBCEF_RENDERER_PLUGINS_CEF_PLUGIN_PLACEHOLDER_H_
+
+#include "components/plugins/renderer/loadable_plugin_placeholder.h"
+#include "content/public/renderer/context_menu_client.h"
+#include "content/public/renderer/render_process_observer.h"
+
+namespace gfx {
+class Size;
+}
+
+enum class CefViewHostMsg_GetPluginInfo_Status;
+
+// This contains information specifying the poster image of plugin placeholders.
+// The default constructor specifies no poster image.
+struct PlaceholderPosterInfo {
+  // The poster image specified in image 'srcset' attribute format.
+  std::string poster_attribute;
+
+  // Used to resolve relative paths in |poster_attribute|.
+  GURL base_url;
+
+  // Specify this to provide partially obscured plugins a centered poster image.
+  gfx::Size custom_poster_size;
+};
+
+class CefPluginPlaceholder final
+    : public plugins::LoadablePluginPlaceholder,
+      public content::RenderProcessObserver,
+      public content::ContextMenuClient,
+      public gin::Wrappable<CefPluginPlaceholder> {
+ public:
+  static gin::WrapperInfo kWrapperInfo;
+
+  static CefPluginPlaceholder* CreateBlockedPlugin(
+      content::RenderFrame* render_frame,
+      blink::WebLocalFrame* frame,
+      const blink::WebPluginParams& params,
+      const content::WebPluginInfo& info,
+      const std::string& identifier,
+      const base::string16& name,
+      int resource_id,
+      const base::string16& message,
+      const PlaceholderPosterInfo& poster_info);
+
+  // Creates a new WebViewPlugin with a MissingPlugin as a delegate.
+  static CefPluginPlaceholder* CreateLoadableMissingPlugin(
+      content::RenderFrame* render_frame,
+      blink::WebLocalFrame* frame,
+      const blink::WebPluginParams& params);
+
+  void SetStatus(CefViewHostMsg_GetPluginInfo_Status status);
+
+ private:
+  CefPluginPlaceholder(content::RenderFrame* render_frame,
+                       blink::WebLocalFrame* frame,
+                       const blink::WebPluginParams& params,
+                       const std::string& html_data,
+                       const base::string16& title);
+  ~CefPluginPlaceholder() override;
+
+  // content::LoadablePluginPlaceholder method
+  blink::WebPlugin* CreatePlugin() override;
+
+  // gin::Wrappable (via PluginPlaceholder) method
+  gin::ObjectTemplateBuilder GetObjectTemplateBuilder(
+      v8::Isolate* isolate) final;
+
+  // content::RenderViewObserver (via PluginPlaceholder) override:
+  bool OnMessageReceived(const IPC::Message& message) override;
+
+  // WebViewPlugin::Delegate (via PluginPlaceholder) methods:
+  v8::Local<v8::Value> GetV8Handle(v8::Isolate* isolate) override;
+  void ShowContextMenu(const blink::WebMouseEvent&) override;
+
+  // content::RenderProcessObserver methods:
+  void PluginListChanged() override;
+
+  // content::ContextMenuClient methods:
+  void OnMenuAction(int request_id, unsigned action) override;
+  void OnMenuClosed(int request_id) override;
+
+  // Javascript callbacks:
+  // Open chrome://plugins in a new tab.
+  void OpenAboutPluginsCallback();
+
+  CefViewHostMsg_GetPluginInfo_Status status_;
+
+  base::string16 title_;
+
+  bool has_host_;
+  int context_menu_request_id_;  // Nonzero when request pending.
+  base::string16 plugin_name_;
+
+  DISALLOW_COPY_AND_ASSIGN(CefPluginPlaceholder);
+};
+
+#endif  // CEF_LIBCEF_RENDERER_PLUGINS_CEF_PLUGIN_PLACEHOLDER_H_