net: Add NET_API to net/base

net/base/backoff_entry.h

Index: net/base/backoff_entry.h
===================================================================
--- net/base/backoff_entry.h	(revision 85332)
+++ net/base/backoff_entry.h	(working copy)
@@ -8,6 +8,7 @@
 
 #include "base/threading/non_thread_safe.h"
 #include "base/time.h"
+#include "net/base/net_api.h"
 
 namespace net {
 
@@ -16,7 +17,8 @@
 //
 // This utility class knows nothing about network specifics; it is
 // intended for reuse in various networking scenarios.
-class BackoffEntry : public base::NonThreadSafe {
+MSVC_SUPPRESS_WARNING(4275)
+class NET_TEST BackoffEntry : public base::NonThreadSafe {
  public:
   // The set of parameters that define a back-off policy.
   struct Policy {