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.

include/cef_context_menu_handler.h

@@ -45,6 +45,30 @@
 
 class CefContextMenuParams;
 
+
+///
+// Callback interface used for continuation of custom context menu display.
+///
+/*--cef(source=library)--*/
+class CefRunContextMenuCallback : public virtual CefBase {
+ public:
+  typedef cef_event_flags_t EventFlags;
+
+  ///
+  // Complete context menu display by selecting the specified |command_id| and
+  // |event_flags|.
+  ///
+  /*--cef(capi_name=cont)--*/
+  virtual void Continue(int command_id, EventFlags event_flags) =0;
+
+  ///
+  // Cancel context menu display.
+  ///
+  /*--cef()--*/
+  virtual void Cancel() =0;
+};
+
+
 ///
 // Implement this interface to handle context menu events. The methods of this
 // class will be called on the UI thread.
@@ -67,6 +91,23 @@ class CefContextMenuHandler : public virtual CefBase {
                                    CefRefPtr<CefContextMenuParams> params,
                                    CefRefPtr<CefMenuModel> model) {}
 
+  ///
+  // Called to allow custom display of the context menu. |params| provides
+  // information about the context menu state. |model| contains the context menu
+  // model resulting from OnBeforeContextMenu. For custom display return true
+  // and execute |callback| either synchronously or asynchronously with the
+  // selected command ID. For default display return false. Do not keep
+  // references to |params| or |model| outside of this callback.
+  ///
+  /*--cef()--*/
+  virtual bool RunContextMenu(CefRefPtr<CefBrowser> browser,
+                              CefRefPtr<CefFrame> frame,
+                              CefRefPtr<CefContextMenuParams> params,
+                              CefRefPtr<CefMenuModel> model,
+                              CefRefPtr<CefRunContextMenuCallback> callback) {
+    return false;
+  }
+
   ///
   // Called to execute a command selected from the context menu. Return true if
   // the command was handled or false for the default implementation. See
@@ -226,6 +267,19 @@ class CefContextMenuParams : public virtual CefBase {
   ///
   /*--cef(default_retval=CM_EDITFLAG_NONE)--*/
   virtual EditStateFlags GetEditStateFlags() =0;
+
+  ///
+  // Returns true if the context menu contains items specified by the renderer
+  // process (for example, plugin placeholder or pepper plugin menu items).
+  ///
+  /*--cef()--*/
+  virtual bool IsCustomMenu() =0;
+
+  ///
+  // Returns true if the context menu was invoked from a pepper plugin.
+  ///
+  /*--cef()--*/
+  virtual bool IsPepperMenu() =0;
 };
 
 #endif  // CEF_INCLUDE_CEF_CONTEXT_MENU_HANDLER_H_