Cleanup: Remove unneeded browser_thread.h includes in contents.

content/public/browser/utility_process_host.h

Index: content/public/browser/utility_process_host.h
===================================================================
--- content/public/browser/utility_process_host.h	(revision 174830)
+++ content/public/browser/utility_process_host.h	(working copy)
@@ -7,11 +7,14 @@
 
 #include "base/process_util.h"
 #include "content/common/content_export.h"
-#include "content/public/browser/browser_thread.h"
 #include "ipc/ipc_sender.h"
 
 class FilePath;
 
+namespace base {
+class SequencedTaskRunner;
+}
+
 namespace content {
 class UtilityProcessHostClient;
 struct ChildProcessData;