Add "dumpsys diskstats" to get a dump of disk-free values.

Also includes a trivial test of I/O latency.  (Mostly useful to be invoked
from checkin to poll disk-free and latency issues.  Also moderately useful
to see in a bugreport.)

Also make "dumpsys netstat" a non-no-op, in case we want this data.

Change-Id: Ia93550a23ca6b35586c5d9217890ee0a5801aae1

services/java/com/android/server/SystemServer.java

@@ -399,6 +399,13 @@ class ServerThread extends Thread {
             } catch (Throwable e) {
                 Slog.e(TAG, "Failure installing status bar icons", e);
             }
+
+            try {
+                Slog.i(TAG, "DiskStats Service");
+                ServiceManager.addService("diskstats", new DiskStatsService(context));
+            } catch (Throwable e) {
+                Slog.e(TAG, "Failure starting DiskStats Service", e);
+            }
         }
 
         // make sure the ADB_ENABLED setting value matches the secure property value