Fix network service hanging with empty bodies.

mojo/public/cpp/bindings/sync_call_restrictions.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_SYNC_CALL_RESTRICTIONS_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_SYNC_CALL_RESTRICTIONS_H_
 
 #include "base/macros.h"
 #include "base/threading/thread_restrictions.h"
 #include "mojo/public/cpp/bindings/bindings_export.h"
 
 #if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON))
 #define ENABLE_SYNC_CALL_RESTRICTIONS 1
 #else
 #define ENABLE_SYNC_CALL_RESTRICTIONS 0
 #endif
 
+namespace content {
+class BrowserTestBase;
+}
+
 namespace display {
 class ForwardingDisplayDelegate;
 }
 
 namespace leveldb {
 class LevelDBMojoProxy;
 }
 
 namespace prefs {
 class PersistentPrefStoreClient;
@@ skipping 26 matching lines @@
 #if ENABLE_SYNC_CALL_RESTRICTIONS
   // Checks whether the current thread is allowed to make sync calls, and causes
   // a DCHECK if not.
   static void AssertSyncCallAllowed();
 #else
   // Inline the empty definitions of functions so that they can be compiled out.
   static void AssertSyncCallAllowed() {}
 #endif
 
  private:
+  // Test-only.

[yzshen1, 2017/06/05 21:07:04]

Does it make sense to move line 68-69 into the "BEGIN/END ALLOWED USAGE"
section?

[jam, 2017/06/06 00:15:47]

Done.

+  friend class content::BrowserTestBase;
   // DO NOT ADD ANY OTHER FRIEND STATEMENTS, talk to mojo/OWNERS first.
   // BEGIN ALLOWED USAGE.
   friend class ui::Gpu;  // http://crbug.com/620058
   // LevelDBMojoProxy makes same-process sync calls from the DB thread.
   friend class leveldb::LevelDBMojoProxy;
   // Pref service connection is sync at startup.
   friend class prefs::PersistentPrefStoreClient;
 
   // END ALLOWED USAGE.
 
@@ skipping 33 matching lines @@
 
     DISALLOW_COPY_AND_ASSIGN(ScopedAllowSyncCall);
   };
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(SyncCallRestrictions);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_SYNC_CALL_RESTRICTIONS_H_