Hook up the SequencedWorkerPool to the browser thread.

content/browser/browser_main_loop.cc

Index: content/browser/browser_main_loop.cc
===================================================================
--- content/browser/browser_main_loop.cc	(revision 117955)
+++ content/browser/browser_main_loop.cc	(working copy)
@@ -500,6 +500,14 @@
     }
   }
 
+  // Close the blocking I/O pool after the other threads. Other threads such
+  // as the I/O thread may need to schedule work like closing files or flushing
+  // data during shutdown, so the blocking pool needs to be available. There
+  // may also be slow operations pending that will blcok shutdown, so closing
+  // it here (which will block until required operations are complete) gives
+  // more head start for those operations to finish.
+  BrowserThreadImpl::ShutdownThreadPool();
+
   if (parts_.get())
     parts_->PostDestroyThreads();
 }