metricsd: Use system properties to store build time metadata.

Instead of using /etc/lsb-release to store the version, channel and
build_target_id, use the Android system properties.

BUG: 22879642

Change-Id: Ic79e74bd14bf8e2c55549c08963a66700b49b544
diff --git a/metricsd/constants.h b/metricsd/constants.h
index 56dac0d..15c15d9 100644
--- a/metricsd/constants.h
+++ b/metricsd/constants.h
@@ -24,6 +24,11 @@
 static const char kMetricsServer[] = "https://clients4.google.com/uma/v2";
 static const char kConsentFilePath[] = "/data/misc/metrics/enabled";
 static const char kDefaultVersion[] = "0.0.0.0";
+
+// System properties used.
+static const char kBuildTargetIdProperty[] = "ro.product.build_target_id";
+static const char kChannelProperty[] = "ro.product.channel";
+static const char kProductVersionProperty[] = "ro.product.version";
 }  // namespace metrics
 
 #endif  // METRICS_CONSTANTS_H_