Improve watchdog error reporting.

We now keep track of all the threads that are stopped, and
print stacks for all of them.  Also more threads are now adding
themselves to the watchdog.

Unfortunately the stack we get from threads is far less useful
than the stacks from the ANR report, because these don't include
any information about the lock the thread is blocked on and what
thread is holding that lock.  For example, here is a test of the
log output from causing a hang in the system process:

W/Watchdog( 5205): *** WATCHDOG KILLING SYSTEM PROCESS: com.android.server.am.ActivityManagerService, main thread
W/Watchdog( 5205): foreground thread stack trace:
W/Watchdog( 5205):     at com.android.server.am.ActivityManagerService.monitor(ActivityManagerService.java:14333)
W/Watchdog( 5205):     at com.android.server.Watchdog$HandlerChecker.run(Watchdog.java:142)
W/Watchdog( 5205):     at android.os.Handler.handleCallback(Handler.java:730)
W/Watchdog( 5205):     at android.os.Handler.dispatchMessage(Handler.java:92)
W/Watchdog( 5205):     at android.os.Looper.loop(Looper.java:137)
W/Watchdog( 5205):     at android.os.HandlerThread.run(HandlerThread.java:61)
W/Watchdog( 5205): main thread stack trace:
W/Watchdog( 5205):     at com.android.server.am.ActivityManagerService.broadcastIntent(ActivityManagerService.java:12252)
W/Watchdog( 5205):     at android.app.ContextImpl.sendBroadcastAsUser(ContextImpl.java:1158)
W/Watchdog( 5205):     at com.android.server.DropBoxManagerService$3.handleMessage(DropBoxManagerService.java:161)
W/Watchdog( 5205):     at android.os.Handler.dispatchMessage(Handler.java:99)
W/Watchdog( 5205):     at android.os.Looper.loop(Looper.java:137)
W/Watchdog( 5205):     at com.android.server.ServerThread.initAndLoop(SystemServer.java:1050)
W/Watchdog( 5205):     at com.android.server.SystemServer.init2(SystemServer.java:1125)
W/Watchdog( 5205):     at com.android.server.SystemServer.init1(Native Method)
W/Watchdog( 5205):     at com.android.server.SystemServer.main(SystemServer.java:1116)
W/Watchdog( 5205):     at java.lang.reflect.Method.invokeNative(Native Method)
W/Watchdog( 5205):     at java.lang.reflect.Method.invoke(Method.java:525)
W/Watchdog( 5205):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:774)
W/Watchdog( 5205):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
W/Watchdog( 5205):     at dalvik.system.NativeStart.main(Native Method)
I/Process ( 5205): Sending signal. PID: 5205 SIG: 9

Change-Id: I8ff9892d8d072d8dc599a73de4bdb75e3b1a6e97