metricsd: Collect generic stats about the system.

Collect memory usage and disk IO statistics periodically.
Also update the Android.mk file to use clang by default.

BUG: 22953719
TEST: builds on external and internal branches.

Change-Id: I1ee3683d014586cf7f711d2e090a99429752063c
diff --git a/metricsd/metrics_daemon.h b/metricsd/metrics_daemon.h
index 9180e23..7f7ea63 100644
--- a/metricsd/metrics_daemon.h
+++ b/metricsd/metrics_daemon.h
@@ -45,6 +45,7 @@
             bool uploader_active,
             bool dbus_enabled,
             MetricsLibraryInterface* metrics_lib,
+            const std::string& diskstats_path,
             const std::string& cpuinfo_max_freq_path,
             const std::string& scaling_max_freq_path,
             const base::TimeDelta& upload_interval,
@@ -78,6 +79,7 @@
   FRIEND_TEST(MetricsDaemonTest, GetHistogramPath);
   FRIEND_TEST(MetricsDaemonTest, IsNewEpoch);
   FRIEND_TEST(MetricsDaemonTest, MessageFilter);
+  FRIEND_TEST(MetricsDaemonTest, ParseDiskStats);
   FRIEND_TEST(MetricsDaemonTest, ParseVmStats);
   FRIEND_TEST(MetricsDaemonTest, ProcessKernelCrash);
   FRIEND_TEST(MetricsDaemonTest, ProcessMeminfo);
@@ -86,7 +88,6 @@
   FRIEND_TEST(MetricsDaemonTest, ProcessUserCrash);
   FRIEND_TEST(MetricsDaemonTest, ReportCrashesDailyFrequency);
   FRIEND_TEST(MetricsDaemonTest, ReadFreqToInt);
-  FRIEND_TEST(MetricsDaemonTest, ReportDiskStats);
   FRIEND_TEST(MetricsDaemonTest, ReportKernelCrashInterval);
   FRIEND_TEST(MetricsDaemonTest, ReportUncleanShutdownInterval);
   FRIEND_TEST(MetricsDaemonTest, ReportUserCrashInterval);
@@ -324,6 +325,7 @@
   scoped_ptr<PersistentInteger> unclean_shutdowns_daily_count_;
   scoped_ptr<PersistentInteger> unclean_shutdowns_weekly_count_;
 
+  std::string diskstats_path_;
   std::string scaling_max_freq_path_;
   std::string cpuinfo_max_freq_path_;