Reduce/remove usage of BrowserThread in content/browser/loader.

content/browser/loader/resource_message_filter.h

Index: content/browser/loader/resource_message_filter.h
diff --git a/content/browser/loader/resource_message_filter.h b/content/browser/loader/resource_message_filter.h
index 45c4e2b74b90fe0d5bec4cb23dc0e1e568a1fcca..21d0fd7b9eda133282af4440d8871f411695b715 100644
--- a/content/browser/loader/resource_message_filter.h
+++ b/content/browser/loader/resource_message_filter.h
@@ -16,7 +16,6 @@
 #include "content/common/url_loader_factory.mojom.h"
 #include "content/public/browser/browser_associated_interface.h"
 #include "content/public/browser/browser_message_filter.h"
-#include "content/public/browser/browser_thread.h"
 #include "content/public/common/resource_type.h"
 
 namespace storage {
@@ -89,7 +88,6 @@ class CONTENT_EXPORT ResourceMessageFilter
   ~ResourceMessageFilter() override;
 
  private:
-  friend struct BrowserThread::DeleteOnThread<BrowserThread::IO>;
   friend class base::DeleteHelper<ResourceMessageFilter>;
 
   // Initializes the weak pointer of this filter in |requester_info_|.