Add Validation logging.

Persist the last 20 lines of validation info for the last 10
networks.

bug: 21599856
Change-Id: I8124480cc9181eea2adb7eb6eabcd07c9506b6d3

core/java/android/util/LocalLog.java

@@ -54,4 +54,18 @@ public final class LocalLog {
             pw.println(itr.next());
         }
     }
+
+    public static class ReadOnlyLocalLog {
+        private final LocalLog mLog;
+        ReadOnlyLocalLog(LocalLog log) {
+            mLog = log;
+        }
+        public void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
+            mLog.dump(fd, pw, args);
+        }
+    }
+
+    public ReadOnlyLocalLog readOnlyLocalLog() {
+        return new ReadOnlyLocalLog(this);
+    }
 }