Remove the file thread dependency from FileNetLogObserver.

components/cronet/android/cronet_library_loader.cc

Index: components/cronet/android/cronet_library_loader.cc
diff --git a/components/cronet/android/cronet_library_loader.cc b/components/cronet/android/cronet_library_loader.cc
index b7aa07aaee65805142793d308678223118a50447..5c94e9f655ddcb3e34b252becca182a0a89ee67b 100644
--- a/components/cronet/android/cronet_library_loader.cc
+++ b/components/cronet/android/cronet_library_loader.cc
@@ -18,6 +18,7 @@
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/statistics_recorder.h"
+#include "base/task_scheduler/task_scheduler.h"
 #include "components/cronet/android/cronet_bidirectional_stream_adapter.h"
 #include "components/cronet/android/cronet_jni_registration.h"
 #include "components/cronet/android/cronet_upload_data_stream_adapter.h"
@@ -67,6 +68,8 @@ bool RegisterJNI(JNIEnv* env) {
 bool NativeInit() {
   if (!base::android::OnJNIOnLoadInit())
     return false;
+  base::TaskScheduler::CreateAndStartWithDefaultParams("Cronet");

[mmenke, 2017/07/06 01:50:01]

I don't think we want to create another thread in Cronet.

[mmenke, 2017/07/06 15:22:26]

I think we'll need to talk about the Cronet folks about what to do here, if we
want to use the task scheduler on Cronet at all - it looks like there's no way
to tell the task scheduler to only use 1 or 2 threads total.  Instead, we tell
it the max number of threads of each type, for 4 different thread types, meaning
a minimum of 4 threads (Though it can stop them when idle).

[mef, 2017/07/06 19:53:01]

Good point. 
I didn't realize that base::TaskScheduler::CreateAndStartWithDefaultParams()
creates a bunch of threads. 
It seems like a way of the future though, right? 
Maybe Cronet should create task scheduler with custom params?

+
   url::Initialize();
   // Initializes the statistics recorder system. This needs to be done before
   // emitting histograms to prevent memory leaks (crbug.com/707836).
@@ -97,6 +100,9 @@ jint CronetOnLoad(JavaVM* vm, void* reserved) {
 }
 
 void CronetOnUnLoad(JavaVM* jvm, void* reserved) {
+  if (base::TaskScheduler::GetInstance())
+    base::TaskScheduler::GetInstance()->Shutdown();
+
   base::android::LibraryLoaderExitHook();
 }