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/cpptoc/context_menu_params_cpptoc.cc

@@ -308,6 +308,36 @@ cef_context_menu_edit_state_flags_t CEF_CALLBACK context_menu_params_get_edit_st
   return _retval;
 }
 
+int CEF_CALLBACK context_menu_params_is_custom_menu(
+    struct _cef_context_menu_params_t* self) {
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self)
+    return 0;
+
+  // Execute
+  bool _retval = CefContextMenuParamsCppToC::Get(self)->IsCustomMenu();
+
+  // Return type: bool
+  return _retval;
+}
+
+int CEF_CALLBACK context_menu_params_is_pepper_menu(
+    struct _cef_context_menu_params_t* self) {
+  // AUTO-GENERATED CONTENT - DELETE THIS COMMENT BEFORE MODIFYING
+
+  DCHECK(self);
+  if (!self)
+    return 0;
+
+  // Execute
+  bool _retval = CefContextMenuParamsCppToC::Get(self)->IsPepperMenu();
+
+  // Return type: bool
+  return _retval;
+}
+
 }  // namespace
 
 
@@ -336,6 +366,8 @@ CefContextMenuParamsCppToC::CefContextMenuParamsCppToC() {
   GetStruct()->is_spell_check_enabled =
       context_menu_params_is_spell_check_enabled;
   GetStruct()->get_edit_state_flags = context_menu_params_get_edit_state_flags;
+  GetStruct()->is_custom_menu = context_menu_params_is_custom_menu;
+  GetStruct()->is_pepper_menu = context_menu_params_is_pepper_menu;
 }
 
 template<> CefRefPtr<CefContextMenuParams> CefCppToC<CefContextMenuParamsCppToC,