Remove all but one use of WeakPtrFactory::DetachFromThread.

chrome/browser/io_thread.cc

Index: chrome/browser/io_thread.cc
diff --git a/chrome/browser/io_thread.cc b/chrome/browser/io_thread.cc
index 568734b54ddcebc7c0f8287c003f4887d723c02c..527cc3eab8a3b455a47c8e540eabd4410041d227 100644
--- a/chrome/browser/io_thread.cc
+++ b/chrome/browser/io_thread.cc
@@ -584,11 +584,6 @@ void IOThread::Init() {
                           FROM_HERE,
                           base::Bind(&IOThread::InitSystemRequestContext,
                                      weak_factory_.GetWeakPtr()));
-
-  // We constructed the weak pointer on the IO thread but it will be
-  // used on the UI thread.  Call this to avoid a thread checker
-  // error.
-  weak_factory_.DetachFromThread();
 }
 
 void IOThread::CleanUp() {