logd: Add control statistics enable/disable.

- ro.build.type=user turn off statistics
- ro.config.low_ram=true turn off statistics
- logd.statistics override

Bug: 17526159
Bug: 17526187
Change-Id: I74796043ac34753c6dd10018719ebc0bcd94e00f
diff --git a/logd/README.property b/logd/README.property
index f4b3c3c..b7fcece 100644
--- a/logd/README.property
+++ b/logd/README.property
@@ -4,6 +4,9 @@
 logd.auditd                 bool  true   Enable selinux audit daemon
 logd.auditd.dmesg           bool  true   selinux audit messages duplicated and
                                          sent on to dmesg log
+logd.statistics             bool depends Enable logcat -S statistics.
+ro.config.low_ram           bool  false  if true, logd.statistics default false
+ro.build.type               string       if user, logd.statistics default false
 logd.statistics.dgram_qlen  bool  false  Record dgram_qlen statistics. This
                                          represents a performance impact and
                                          is used to determine the platform's