For #17816: add profiler marker for onPreDraw via HomeActivity.onStart.

This may be useful for MAIN start up to determine when the user begins
seeing content.

app/src/main/java/org/mozilla/fenix/HomeActivity.kt

@@ -92,6 +92,7 @@ import org.mozilla.fenix.library.history.HistoryFragmentDirections
 import org.mozilla.fenix.library.recentlyclosed.RecentlyClosedFragmentDirections
 import org.mozilla.fenix.perf.Performance
 import org.mozilla.fenix.perf.PerformanceInflater
+import org.mozilla.fenix.perf.ProfilerMarkers
 import org.mozilla.fenix.perf.StartupTimeline
 import org.mozilla.fenix.search.SearchDialogFragmentDirections
 import org.mozilla.fenix.session.PrivateNotificationService
@@ -327,6 +328,8 @@ open class HomeActivity : LocaleAwareAppCompatActivity(), NavHostActivity {
         breadcrumb(
             message = "onStart()"
         )
+
+        ProfilerMarkers.homeActivityOnStart(rootContainer, components.core.engine.profiler)
     }
 
     override fun onStop() {

app/src/main/java/org/mozilla/fenix/perf/ProfilerMarkers.kt

@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.fenix.perf
+
+import android.view.View
+import androidx.core.view.doOnPreDraw
+import mozilla.components.concept.base.profiler.Profiler
+
+/**
+ * A container for functions for when adding a profiler marker is less readable
+ * (e.g. multiple lines, more advanced logic).
+ */
+object ProfilerMarkers {
+
+    fun homeActivityOnStart(rootContainer: View, profiler: Profiler?) {
+        rootContainer.doOnPreDraw {
+            profiler?.addMarker("onPreDraw", "expected first frame via HomeActivity.onStart")
+        }
+    }
+}