[cronet] make startNetLogToFile write to correct file

components/cronet/ios/cronet_environment.mm

Index: components/cronet/ios/cronet_environment.mm
diff --git a/components/cronet/ios/cronet_environment.mm b/components/cronet/ios/cronet_environment.mm
index 101e1f4db64ca8b5a470571b7999ed2d96389537..d1624c3de12c2bd1d1a1b5e624fe984029cabbc0 100644
--- a/components/cronet/ios/cronet_environment.mm
+++ b/components/cronet/ios/cronet_environment.mm
@@ -144,34 +144,36 @@ void CronetEnvironment::Initialize() {
   g_network_change_notifier = net::NetworkChangeNotifier::Create();
 }
 
-void CronetEnvironment::StartNetLog(base::FilePath::StringType file_name,
+bool CronetEnvironment::StartNetLog(base::FilePath::StringType file_name,
                                     bool log_bytes) {
-  DCHECK(file_name.length());
-  PostToNetworkThread(FROM_HERE,
-                      base::Bind(&CronetEnvironment::StartNetLogOnNetworkThread,
-                                 base::Unretained(this), file_name, log_bytes));
+  if (!file_name.length())
+    return false;
+
+  base::FilePath path(file_name);
+
+  base::ScopedFILE file(base::OpenFile(path, "w"));
+  if (!file) {
+    LOG(ERROR) << "Can not start NetLog to " << path.value() << ": "
+               << strerror(errno);
+    return false;
+  }
+
+  LOG(WARNING) << "Starting NetLog to " << path.value();
+  PostToNetworkThread(
+      FROM_HERE,
+      base::Bind(&CronetEnvironment::StartNetLogOnNetworkThread,
+                 base::Unretained(this), base::Passed(&file), log_bytes));
+
+  return true;
 }
 
-void CronetEnvironment::StartNetLogOnNetworkThread(
-    const base::FilePath::StringType& file_name,
-    bool log_bytes) {
-  DCHECK(file_name.length());
+void CronetEnvironment::StartNetLogOnNetworkThread(base::ScopedFILE file,
+                                                   bool log_bytes) {
   DCHECK(net_log_);
 
   if (net_log_observer_)
     return;
 
-  base::FilePath files_root;
-  if (!PathService::Get(base::DIR_HOME, &files_root))
-    return;
-
-  base::FilePath full_path = files_root.Append(file_name);
-  base::ScopedFILE file(base::OpenFile(full_path, "w"));
-  if (!file) {
-    LOG(ERROR) << "Can not start NetLog to " << full_path.value();
-    return;
-  }
-
   net::NetLogCaptureMode capture_mode =
       log_bytes ? net::NetLogCaptureMode::IncludeSocketBytes()
                 : net::NetLogCaptureMode::Default();
@@ -180,7 +182,7 @@ void CronetEnvironment::StartNetLogOnNetworkThread(
   net_log_observer_->set_capture_mode(capture_mode);
   net_log_observer_->StartObserving(main_context_->net_log(), std::move(file),
                                     nullptr, main_context_.get());
-  LOG(WARNING) << "Started NetLog to " << full_path.value();
+  LOG(WARNING) << "Started NetLog";
 }
 
 void CronetEnvironment::StopNetLog() {