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

services/java/com/android/server/NetworkTimeUpdateService.java

@@ -27,7 +27,6 @@ import android.database.ContentObserver;
 import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
 import android.os.Handler;
-import android.os.HandlerThread;
 import android.os.Looper;
 import android.os.Message;
 import android.os.SystemClock;
@@ -36,6 +35,7 @@ import android.util.Log;
 import android.util.NtpTrustedTime;
 import android.util.TrustedTime;
 
+import com.android.internal.os.BackgroundThread;
 import com.android.internal.telephony.TelephonyIntents;
 
 /**
@@ -71,7 +71,6 @@ public class NetworkTimeUpdateService {
 
     // NTP lookup is done on this thread and handler
     private Handler mHandler;
-    private HandlerThread mThread;
     private AlarmManager mAlarmManager;
     private PendingIntent mPendingPollIntent;
     private SettingsObserver mSettingsObserver;
@@ -114,9 +113,7 @@ public class NetworkTimeUpdateService {
         registerForAlarms();
         registerForConnectivityIntents();
 
-        mThread = new HandlerThread(TAG);
-        mThread.start();
-        mHandler = new MyHandler(mThread.getLooper());
+        mHandler = new MyHandler(BackgroundThread.get().getLooper());
         // Check the network time on the new thread
         mHandler.obtainMessage(EVENT_POLL_NETWORK_TIME).sendToTarget();