Cherry pick PR #769: Document metrics setting persistence in IDL file…

… (#819)

b/286898092

Change-Id: I84882161c51113859ceb11f8cdd2250aff666de7
(cherry picked from commit 0da3ca6)

Co-authored-by: Joel Martinez <joeltine@google.com>

cobalt/h5vcc/h5vcc_metrics.idl

@@ -34,8 +34,10 @@ interface H5vccMetrics {
   // Enable Cobalt metrics logging. Metrics are disabled by default and should
   // be enabled as soon as possible. When enabled, at regular intervals, the
   // bound onMetricEvent callback will be called with telemetry payloads to
-  // be uploaded and logged on the server.
-  // TODO(b/286898092): Update docs here when setting is persistent.
+  // be uploaded and logged on the server. Both the enable/disable settings
+  // are persistent or "sticky". That is, you only have to call them once
+  // and that setting will persist through multiple app lifecycles until the
+  // enable/disable APIs are explicitly called again.
   void enable();
 
   // Disable Cobalt metrics logging. If disabled, the metric event handler
@@ -52,7 +54,9 @@ interface H5vccMetrics {
 
   // Sets the frequency in which Cobalt metrics will be snapshotted and sent to
   // the metric event handler. Defaults to 5 minutes if not set. Must be > 0,
-  // else will be ignored.
+  // else will be ignored. This setting is persistent. That is, it's "sticky"
+  // and will be persisted through multiple app lifetimes unless it's called
+  // again with a different value.
   void setMetricEventInterval(unsigned long intervalSeconds);
 };