Revert of Reland: Lazily initialize MessageLoop for faster thread startup

content/public/browser/browser_thread_delegate.h

Index: content/public/browser/browser_thread_delegate.h
diff --git a/content/public/browser/browser_thread_delegate.h b/content/public/browser/browser_thread_delegate.h
index 3688e656e73bb119df5271d68c0702b5bfa01bf0..ad5fd7e57eba160f8618d46a9823fa5e6bbc60ee 100644
--- a/content/public/browser/browser_thread_delegate.h
+++ b/content/public/browser/browser_thread_delegate.h
@@ -22,6 +22,9 @@
   // Called prior to starting the message loop
   virtual void Init() = 0;
 
+  // Called as the first task on the thread's message loop.
+  virtual void InitAsync() = 0;
+
   // Called just after the message loop ends.
   virtual void CleanUp() = 0;
 };