Use FileNetLogObserver for implementing --log-net-log.

net/log/file_net_log_observer_unittest.cc

 // 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.
 
 #include "net/log/file_net_log_observer.h"
 
 #include <math.h>
 
 #include <memory>
 #include <string>
@@ skipping 266 matching lines @@
   // Send dummy event
   AddEntries(logger_.get(), 1, kDummyEventSize);
 
   // The log files should have been started.
   ASSERT_TRUE(LogFilesExist());
 
   logger_.reset();
 
   // When the logger is re-set without having called StopObserving(), the
   // partially written log files are deleted.
   ASSERT_FALSE(LogFilesExist());

[mmenke, 2017/07/06 21:31:29]

How is this guaranteed?  Deletion occurs on another thread.

[eroman, 2017/07/06 21:57:54]

This is guaranteed by the changes I made in the dependent CL, which has
LogFilesExist() calling:

base::TaskScheduler::GetInstance()->FlushForTesting();

In order to ensure the file I/O has completed.

(And the task having been posted by that point is a bit of an implementation
assumption. In fact the task will have been posted for the initialization, not
for the preceding "AddEntries()" call as that doesn't add enough entries to
cause a flush).

 }
 
+// Tests calling StopObserving() with a null closure.
+TEST_P(FileNetLogObserverTest, StopObservingNullClosure) {
+  CreateAndStartObserving(nullptr);
+
+  // Send dummy event
+  AddEntries(logger_.get(), 1, kDummyEventSize);
+
+  // The log files should have been started.
+  ASSERT_TRUE(LogFilesExist());

[mmenke, 2017/07/06 21:31:29]

How is this guaranteed?  The file is created on another thread.

[eroman, 2017/07/06 21:57:54]

same explanation as above.

+
+  logger_->StopObserving(nullptr, base::OnceClosure());
+
+  logger_.reset();
+
+  // Since the logger was explicitly stopped, its files should still exist.
+  ASSERT_TRUE(LogFilesExist());
+}
+
 TEST_P(FileNetLogObserverTest, GeneratesValidJSONWithNoEvents) {
   TestClosure closure;
 
   CreateAndStartObserving(nullptr);
 
   logger_->StopObserving(nullptr, closure.closure());
 
   closure.WaitForResult();
 
   std::unique_ptr<base::Value> root;
@@ skipping 561 matching lines @@
   // Join all the threads.
   threads.clear();
 
   // The log file doesn't exist since StopObserving() was not called.
   ASSERT_FALSE(LogFilesExist());
 }
 
 }  // namespace
 
 }  // namespace net