Don't write to --log-net-log from MojoNetLog when running in-process.

Bug: 745877
Change-Id: I05d3fcdbe55509d808f0ab696b159ca22876a0b8
Reviewed-on: https://chromium-review.googlesource.com/576358Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487621}

content/network/network_service_impl.cc

@@ -25,15 +25,18 @@ std::unique_ptr<NetworkService> NetworkService::Create() {
 
 class NetworkServiceImpl::MojoNetLog : public net::NetLog {
  public:
-  MojoNetLog() {
-    const base::CommandLine* command_line =
-        base::CommandLine::ForCurrentProcess();
+  MojoNetLog() {}
 
   // If specified by the command line, stream network events (NetLog) to a
   // file on disk. This will last for the duration of the process.
-    if (command_line->HasSwitch(switches::kLogNetLog)) {
+  void ProcessCommandLine(const base::CommandLine& command_line) {
+    if (!command_line.HasSwitch(switches::kLogNetLog))
+      return;
+
     base::FilePath log_path =
-          command_line->GetSwitchValuePath(switches::kLogNetLog);
+        command_line.GetSwitchValuePath(switches::kLogNetLog);
+
+    // TODO(eroman): Should get capture mode from the command line.
     net::NetLogCaptureMode capture_mode =
         net::NetLogCaptureMode::IncludeCookiesAndCredentials();
 
@@ -41,7 +44,7 @@ class NetworkServiceImpl::MojoNetLog : public net::NetLog {
         net::FileNetLogObserver::CreateUnbounded(log_path, nullptr);
     file_net_log_observer_->StartObserving(this, capture_mode);
   }
-  }
+
   ~MojoNetLog() override {
     if (file_net_log_observer_)
       file_net_log_observer_->StopObserving(nullptr, base::OnceClosure());
@@ -62,6 +65,11 @@ NetworkServiceImpl::NetworkServiceImpl(
   if (registry_) {
     registry_->AddInterface<mojom::NetworkService>(
         base::Bind(&NetworkServiceImpl::Create, base::Unretained(this)));
+
+    // Note: The command line switches are only checked when running out of
+    // process, since in in-process mode other code may already be writing to
+    // the destination log file.
+    net_log_->ProcessCommandLine(*base::CommandLine::ForCurrentProcess());
   }
 }