fix(extensions): set lowest isolated world id (#22212)

* fix(extensions): set lowest isolated world id

* refactor: move world IDs into separate header file

Several files are including electron_render_frame_observer.h just for the world IDs.

shell/common/world_ids.h

@@ -0,0 +1,31 @@
+// Copyright (c) 2020 Samuel Maddock
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef SHELL_COMMON_WORLD_IDS_H_
+#define SHELL_COMMON_WORLD_IDS_H_
+
+#include "third_party/blink/public/platform/web_isolated_world_ids.h"
+
+namespace electron {
+
+enum WorldIDs : int32_t {
+  MAIN_WORLD_ID = 0,
+
+  // Use a high number far away from 0 to not collide with any other world
+  // IDs created internally by Chrome.
+  ISOLATED_WORLD_ID = 999,
+
+  // Numbers for isolated worlds for extensions are set in
+  // lib/renderer/content-script-injector.ts, and are greater than or equal to
+  // this number, up to ISOLATED_WORLD_ID_EXTENSIONS_END.
+  ISOLATED_WORLD_ID_EXTENSIONS = 1 << 20,
+
+  // Last valid isolated world ID.
+  ISOLATED_WORLD_ID_EXTENSIONS_END =
+      blink::IsolatedWorldId::kEmbedderWorldIdLimit - 1
+};
+
+}  // namespace electron
+
+#endif  // SHELL_COMMON_WORLD_IDS_H_