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/plugin_preroller.h

@@ -0,0 +1,61 @@
+// 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.
+
+#ifndef CEF_LIBCEF_RENDERER_PLUGINS_PLUGIN_PREROLLER_H_
+#define CEF_LIBCEF_RENDERER_PLUGINS_PLUGIN_PREROLLER_H_
+
+#include "base/macros.h"
+#include "content/public/common/webplugininfo.h"
+#include "content/public/renderer/plugin_instance_throttler.h"
+#include "content/public/renderer/render_frame_observer.h"
+#include "third_party/WebKit/public/web/WebPluginParams.h"
+#include "url/gurl.h"
+
+namespace blink {
+class WebLocalFrame;
+class WebPlugin;
+}
+
+class SkBitmap;
+
+// This class manages a plugin briefly for the purposes of keyframe extraction.
+// Once a keyframe has been extracted, this class will replace the plugin with
+// a ChromePluginPlaceholder. The actual plugin will continue to live in a
+// throttled state. This class manages its own lifetime.
+class CefPluginPreroller : public content::PluginInstanceThrottler::Observer,
+                           public content::RenderFrameObserver {
+ public:
+  // Does not take ownership of either |plugin| or |throttler|.
+  CefPluginPreroller(content::RenderFrame* render_frame,
+                     blink::WebLocalFrame* frame,
+                     const blink::WebPluginParams& params,
+                     const content::WebPluginInfo& info,
+                     const std::string& identifier,
+                     const base::string16& name,
+                     const base::string16& message,
+                     content::PluginInstanceThrottler* throttler);
+
+  ~CefPluginPreroller() override;
+
+ private:
+  // content::PluginInstanceThrottler::Observer methods:
+  void OnKeyframeExtracted(const SkBitmap* bitmap) override;
+  void OnThrottleStateChange() override;
+  void OnThrottlerDestroyed() override;
+
+  blink::WebLocalFrame* frame_;
+  blink::WebPluginParams params_;
+  content::WebPluginInfo info_;
+  std::string identifier_;
+  base::string16 name_;
+  base::string16 message_;
+
+  content::PluginInstanceThrottler* throttler_;
+
+  GURL keyframe_data_url_;
+
+  DISALLOW_COPY_AND_ASSIGN(CefPluginPreroller);
+};
+
+#endif  // CEF_LIBCEF_RENDERER_PLUGINS_PLUGIN_PREROLLER_H_