[Battery]: Delay start of CallStats.

To avoid unnecessary repeating tasks, CallStats' timer is started only
upon Call::EnsureStarted().

Bug: chromium:1152887
Change-Id: I1015315f42127bf510affc3d22c930b20eac8bba
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/206880
Commit-Queue: Tommi <tommi@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33232}
diff --git a/call/call.cc b/call/call.cc
index 6bffbd8..daeead1 100644
--- a/call/call.cc
+++ b/call/call.cc
@@ -686,6 +686,8 @@
   }
   is_started_ = true;
 
+  call_stats_->EnsureStarted();
+
   // This call seems to kick off a number of things, so probably better left
   // off being kicked off on request rather than in the ctor.
   transport_send_ptr_->RegisterTargetTransferRateObserver(this);