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/NativeDaemonConnector.java

@@ -19,7 +19,6 @@ package com.android.server;
 import android.net.LocalSocket;
 import android.net.LocalSocketAddress;
 import android.os.Handler;
-import android.os.HandlerThread;
 import android.os.Message;
 import android.os.SystemClock;
 import android.util.LocalLog;
@@ -81,9 +80,7 @@ final class NativeDaemonConnector implements Runnable, Handler.Callback, Watchdo
 
     @Override
     public void run() {
-        HandlerThread thread = new HandlerThread(TAG + ".CallbackHandler");
+        mCallbackHandler = new Handler(FgThread.get().getLooper(), this);
-        thread.start();
-        mCallbackHandler = new Handler(thread.getLooper(), this);
 
         while (true) {
             try {

services/java/com/android/server/net/NetworkStatsService.java

@@ -96,7 +96,6 @@ import android.os.Binder;
 import android.os.DropBoxManager;
 import android.os.Environment;
 import android.os.Handler;
-import android.os.HandlerThread;
 import android.os.INetworkManagementService;
 import android.os.Message;
 import android.os.PowerManager;
@@ -120,6 +119,7 @@ import com.android.internal.util.ArrayUtils;
 import com.android.internal.util.FileRotator;
 import com.android.internal.util.IndentingPrintWriter;
 import com.android.server.EventLogTags;
+import com.android.server.IoThread;
 import com.android.server.connectivity.Tethering;
 import com.google.android.collect.Maps;
 
@@ -240,7 +240,6 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
     /** Data layer operation counters for splicing into other structures. */
     private NetworkStats mUidOperations = new NetworkStats(0L, 10);
 
-    private final HandlerThread mHandlerThread;
     private final Handler mHandler;
 
     private boolean mSystemReady;
@@ -271,9 +270,7 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
                 Context.POWER_SERVICE);
         mWakeLock = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, TAG);
 
-        mHandlerThread = new HandlerThread(TAG);
+        mHandler = new Handler(IoThread.get().getLooper(), mHandlerCallback);
-        mHandlerThread.start();
-        mHandler = new Handler(mHandlerThread.getLooper(), mHandlerCallback);
 
         mSystemDir = checkNotNull(systemDir);
         mBaseDir = new File(systemDir, "netstats");