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

headless/test/headless_browser_test.h

Index: headless/test/headless_browser_test.h
diff --git a/headless/test/headless_browser_test.h b/headless/test/headless_browser_test.h
index e5e29e5f214f3d2c9bf43455efed183a4528d2e8..f2cae33abbd3f1ba8d94bfea250d654588f79cb9 100644
--- a/headless/test/headless_browser_test.h
+++ b/headless/test/headless_browser_test.h
@@ -123,6 +123,10 @@ class HeadlessAsyncDevTooledBrowserTest : public HeadlessBrowserTest,
   // Whether or not we should request a TabSocket when creating |web_contents_|.
   virtual bool GetCreateTabSocket();
 
+  // Selects between creating the TabSocket only in an isolated world or the
+  // main world.
+  virtual bool GetCreateTabSocketOnlyForIsolatedWorld();
+
  protected:
   void RunTest();