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_dll/ctocpp/context_menu_params_ctocpp.cc

@@ -303,6 +303,34 @@ CefContextMenuParams::EditStateFlags CefContextMenuParamsCToCpp::GetEditStateFla
   return _retval;
 }
 
+bool CefContextMenuParamsCToCpp::IsCustomMenu() {
+  cef_context_menu_params_t* _struct = GetStruct();
+  if (CEF_MEMBER_MISSING(_struct, is_custom_menu))
+    return false;
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  // Execute
+  int _retval = _struct->is_custom_menu(_struct);
+
+  // Return type: bool
+  return _retval?true:false;
+}
+
+bool CefContextMenuParamsCToCpp::IsPepperMenu() {
+  cef_context_menu_params_t* _struct = GetStruct();
+  if (CEF_MEMBER_MISSING(_struct, is_pepper_menu))
+    return false;
+
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  // Execute
+  int _retval = _struct->is_pepper_menu(_struct);
+
+  // Return type: bool
+  return _retval?true:false;
+}
+
 
 // CONSTRUCTOR - Do not edit by hand.