Add changes for cold start logging and TODO for app state change

Author: tejasd

firebase-perf/src/main/java/com/google/firebase/perf/session/FirebasePerformanceSessionSubscriber.kt

@@ -28,12 +28,17 @@ class FirebasePerformanceSessionSubscriber(override val isDataCollectionEnabled:
 
   override fun onSessionChanged(sessionDetails: SessionSubscriber.SessionDetails) {
     val currentPerfSession = SessionManager.getInstance().perfSession()
-    // TODO(b/394127311): Add logic to deal with app start gauges.
     FirebaseSessionsEnforcementCheck.checkSession(currentPerfSession, "onSessionChanged")
 
+    if (currentPerfSession.isLegacy()) {
+      GaugeManager.getInstance().logGaugeMetadata(sessionDetails.sessionId, ApplicationProcessState.FOREGROUND)
+      GaugeManager.getInstance().logExistingGaugeMetrics(sessionDetails.sessionId, ApplicationProcessState.FOREGROUND)
+    }
+
     val updatedSession = PerfSession.createWithId(sessionDetails.sessionId)
     SessionManager.getInstance().updatePerfSession(updatedSession)
     GaugeManager.getInstance()
       .logGaugeMetadata(updatedSession.sessionId(), ApplicationProcessState.FOREGROUND)
+    // TODO(b/394127311): Update app state change and start logging if necessary.
   }
 }

firebase-perf/src/main/java/com/google/firebase/perf/session/PerfSession.java

@@ -30,7 +30,7 @@
 public class PerfSession implements Parcelable {
   private final Timer creationTime;
   private final String sessionId;
-  private boolean isGaugeAndEventCollectionEnabled = false;
+  private boolean isGaugeAndEventCollectionEnabled = true;
 
   /*
    * Creates a PerfSession object and decides what metrics to collect.

firebase-perf/src/main/java/com/google/firebase/perf/session/SessionManager.java

@@ -23,8 +23,6 @@
 import com.google.firebase.perf.logging.FirebaseSessionsEnforcementCheck;
 import com.google.firebase.perf.session.gauges.GaugeManager;
 import com.google.firebase.perf.v1.ApplicationProcessState;
-import com.google.firebase.perf.v1.GaugeMetadata;
-import com.google.firebase.perf.v1.GaugeMetric;
 import java.lang.ref.WeakReference;
 import java.util.HashSet;
 import java.util.Iterator;