dumpsys: add --thread option

This displays the thread usage of services in the format
"<threadsUsed>/<threadCount>". This has been useful in lshal to find
deadlocks in binder threads.

Test: atest dumpsys_test
Test: run 'dumpsys --thread' on cuttlefish and verify thread usage
Test: run 'dumpsys --thread SurfaceFlinger' and verify thread usage
Bug: 140639610
Change-Id: I0cd3f86ca47ec911b276d8e8859ef54743ee34cf
diff --git a/cmds/dumpsys/dumpsys.h b/cmds/dumpsys/dumpsys.h
index 929c55c..349947c 100644
--- a/cmds/dumpsys/dumpsys.h
+++ b/cmds/dumpsys/dumpsys.h
@@ -52,13 +52,14 @@
     static void setServiceArgs(Vector<String16>& args, bool asProto, int priorityFlags);
 
     enum class Type {
-        DUMP,  // dump using `dump` function
-        PID,   // dump pid of server only
+        DUMP,    // dump using `dump` function
+        PID,     // dump pid of server only
+        THREAD,  // dump thread usage of server only
     };
 
     /**
      * Starts a thread to connect to a service and get its dump output. The thread redirects
-     * the output to a pipe. Thread must be stopped by a subsequent callto {@code
+     * the output to a pipe. Thread must be stopped by a subsequent call to {@code
      * stopDumpThread}.
      * @param serviceName
      * @param args list of arguments to pass to service dump method.