Start combining threads in system process.

This introduces four generic thread that services can
use in the system process:

- Background: part of the framework for all processes, for
work that is purely background (no timing constraint).
- UI: for time-critical display of UI.
- Foreground: normal foreground work.
- IO: performing IO operations.

I went through and moved services into these threads in the
places I felt relatively comfortable about understanding what
they are doing.  There are still a bunch more we need to look
at -- lots of networking stuff left, 3 or so different native
daemon connectors which I didn't know how much would block,
audio stuff, etc.

Also updated Watchdog to be aware of and check these new
threads, with a new API for other threads to also participate
in this checking.

Change-Id: Ie2f11061cebde5f018d7383b3a910fbbd11d5e11
diff --git a/services/java/com/android/server/BluetoothManagerService.java b/services/java/com/android/server/BluetoothManagerService.java
index ea7b696..8684e5b 100644
--- a/services/java/com/android/server/BluetoothManagerService.java
+++ b/services/java/com/android/server/BluetoothManagerService.java
@@ -33,7 +33,6 @@
 import android.content.ServiceConnection;
 import android.os.Binder;
 import android.os.Handler;
-import android.os.HandlerThread;
 import android.os.IBinder;
 import android.os.Looper;
 import android.os.Message;
@@ -115,7 +114,6 @@
     // used inside handler thread
     private boolean mEnable;
     private int mState;
-    private HandlerThread mThread;
     private final BluetoothHandler mHandler;
 
     private void registerForAirplaneMode(IntentFilter filter) {
@@ -188,9 +186,7 @@
     };
 
     BluetoothManagerService(Context context) {
-        mThread = new HandlerThread("BluetoothManager");
-        mThread.start();
-        mHandler = new BluetoothHandler(mThread.getLooper());
+        mHandler = new BluetoothHandler(IoThread.get().getLooper());
 
         mContext = context;
         mBluetooth = null;