[Reland] Allow headless TabSocket in isolated worlds & remove obsolete logic

third_party/WebKit/public/platform/WebIsolatedWorldIds.h

+// Copyright 2017 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 WebIsolatedWorldIds_h
+#define WebIsolatedWorldIds_h
+
+namespace blink {
+
+enum IsolatedWorldId {
+  // Embedder isolated worlds can use IDs in [1, 1<<29).
+  kEmbedderWorldIdLimit = (1 << 29),
+  kDocumentXMLTreeViewerWorldId,
+  kDevToolsFirstIsolatedWorldId,
+  kDevToolsLastIsolatedWorldId = kDevToolsFirstIsolatedWorldId + 100,
+  kIsolatedWorldIdLimit,
+};
+
+}  // namespace blink
+
+#endif  // WebIsolatedWorldIds_h