aaudio: name threads for easier debugging

Name them "AAudio_#" where # is an increasing index.
For example AAudio_1, AAudio_2, etc.

Also name threads that are used for sending timestamps.

Test: run write_sine_callback then dump the threads for that process.
Change-Id: Ibd8c7be1109f6c15a4601ef154038cdce2e65e11
diff --git a/services/oboeservice/AAudioThread.h b/services/oboeservice/AAudioThread.h
index 02f1459..ffc9b7b 100644
--- a/services/oboeservice/AAudioThread.h
+++ b/services/oboeservice/AAudioThread.h
@@ -43,7 +43,9 @@
 {
 public:
     AAudioThread();
-    AAudioThread(Runnable *runnable);
+
+    AAudioThread(const char *prefix);
+
     virtual ~AAudioThread() = default;
 
     /**
@@ -66,10 +68,15 @@
     void dispatch(); // called internally from 'C' thread wrapper
 
 private:
-    Runnable    *mRunnable;
-    bool         mHasThread;
+
+    void setup(const char *prefix);
+
+    Runnable    *mRunnable = nullptr;
+    bool         mHasThread = false;
     pthread_t    mThread; // initialized in constructor
 
+    static std::atomic<uint32_t> mNextThreadIndex;
+    char         mName[16]; // max length for a pthread_name
 };
 
 } /* namespace aaudio */