MediaMetricsService: Use system_clock for TimedAction

This ensures AudioPowerUsage atoms are delivered
based on wallclock time.

Test: adb shell dumpsys media.metrics --all
Bug: 314810064
Change-Id: Ic98e6b48602f61792c40b21d57b809596fa136ff
diff --git a/services/mediametrics/AudioPowerUsage.cpp b/services/mediametrics/AudioPowerUsage.cpp
index 630a436..7dc445b 100644
--- a/services/mediametrics/AudioPowerUsage.cpp
+++ b/services/mediametrics/AudioPowerUsage.cpp
@@ -549,7 +549,7 @@
 
     int slot = 1;
     std::stringstream ss;
-    ss << "AudioPowerUsage:\n";
+    ss << "AudioPowerUsage interval " << mIntervalHours << " hours:\n";
     for (const auto &item : mItems) {
         if (slot >= limit - 1) {
             ss << "-- AudioPowerUsage may be truncated!\n";