For mozilla-mobile#7781: instrument visual completeness for top sites.

Eyeballing my output in *Debug builds on my P2, this adds approximately 115ms
or slightly less from first frame drawn to visually complete time.

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

@@ -106,7 +106,6 @@ open class HomeActivity : LocaleAwareAppCompatActivity() {
 
         setupThemeAndBrowsingMode(getModeFromIntentOrLastKnown(intent))
         setContentView(R.layout.activity_home)
-        Performance.instrumentColdStartupToHomescreenTime(this)
 
         externalSourceIntentProcessors.any { it.process(intent, navHost.navController, this.intent) }
 

app/src/main/java/org/mozilla/fenix/home/sessioncontrol/viewholders/topsites/TopSitesAdapter.kt

@@ -10,6 +10,7 @@ import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.ListAdapter
 import mozilla.components.feature.top.sites.TopSite
 import org.mozilla.fenix.home.sessioncontrol.TopSiteInteractor
+import org.mozilla.fenix.perf.ColdStartPerfMonitor
 
 class TopSitesAdapter(
     private val interactor: TopSiteInteractor
@@ -21,6 +22,7 @@ class TopSitesAdapter(
     }
 
     override fun onBindViewHolder(holder: TopSiteItemViewHolder, position: Int) {
+        ColdStartPerfMonitor.onTopSitesItemBound(holder)
         holder.bind(getItem(position))
     }
 

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

@@ -0,0 +1,43 @@
+/* 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 androidx.core.view.doOnPreDraw
+import org.mozilla.fenix.HomeActivity
+import org.mozilla.fenix.home.sessioncontrol.viewholders.topsites.TopSiteItemViewHolder
+
+/**
+ * Functionality related to measuring the performance of cold startup. Note: this is cold startup in
+ * the context of FNPRMS: we have yet to define cold startup in the context of the production app.
+ */
+object ColdStartPerfMonitor {
+
+    private var isVisuallyComplete = false
+
+    /**
+     * Instruments "visually complete" cold startup time to homescreen for use with our internal
+     * measuring system, FNPRMS. This value may also appear in the Google Play Vitals dashboards.
+     *
+     * For FNPRMS, we define "visually complete" to be when top sites is loaded with placeholders;
+     * the animation to display top sites will occur after this point, as will the asynchronous
+     * loading of the actual top sites icons. Our focus for visually complete is usability.
+     * There are no tabs available in our FNPRMS tests so they are ignored for this instrumentation.
+     *
+     * This will need to be rewritten if any parts of the UI are changed to be displayed asynchronously.
+     */
+    fun onTopSitesItemBound(holder: TopSiteItemViewHolder) {
+        if (isVisuallyComplete) { return }
+        isVisuallyComplete = true
+
+        // For greater accuracy, we could add an onDrawListener instead of a preDrawListener but:
+        // - single use onDrawListeners are not built-in and it's non-trivial to write one
+        // - the difference in timing is minimal (< 7ms on Pixel 2)
+        // - if we compare against another app using a preDrawListener, as we are with Fennec, it
+        // should be comparable
+        //
+        // Ideally we wouldn't cast to HomeActivity but we want to save implementation time.
+        holder.itemView.doOnPreDraw { (it.context as HomeActivity).reportFullyDrawn() }
+    }
+}

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

@@ -8,12 +8,9 @@ import android.content.Context
 import android.content.Intent
 import android.content.IntentFilter
 import android.os.BatteryManager
-import androidx.core.view.doOnPreDraw
-import kotlinx.android.synthetic.main.activity_home.*
-import org.mozilla.fenix.HomeActivity
 import org.mozilla.fenix.onboarding.FenixOnboarding
-import android.provider.Settings as AndroidSettings
 import org.mozilla.fenix.utils.Settings
+import android.provider.Settings as AndroidSettings
 
 /**
  * A collection of objects related to app performance.
@@ -22,30 +19,6 @@ object Performance {
     const val TAG = "FenixPerf"
     private const val EXTRA_IS_PERFORMANCE_TEST = "performancetest"
 
-    /**
-     * Instruments cold startup time for use with our internal measuring system, FNPRMS. This may
-     * also appear in Google Play Vitals dashboards.
-     *
-     * This will need to be rewritten if any parts of the UI are changed to be displayed
-     * asynchronously.
-     *
-     * In the current implementation, we only intend to instrument cold startup to the homescreen.
-     * To save implementation time, we ignore the fact that the RecyclerView draws twice if the user
-     * has tabs, collections, etc. open: the "No tabs" placeholder and a tab list. This
-     * instrumentation will only capture the "No tabs" draw.
-     */
-    fun instrumentColdStartupToHomescreenTime(activity: HomeActivity) {
-        // For greater accuracy, we could add an onDrawListener instead of a preDrawListener but:
-        // - single use onDrawListeners are not built-in and it's non-trivial to write one
-        // - the difference in timing is minimal (< 7ms on Pixel 2)
-        // - if we compare against another app using a preDrawListener, it should be comparable
-        //
-        // Unfortunately, this is tightly coupled to the root view of HomeActivity's view hierarchy
-        activity.rootContainer.doOnPreDraw {
-            activity.reportFullyDrawn()
-        }
-    }
-
     /**
      * Processes intent for Performance testing to remove protection pop up ( but keeps the TP
      * on) and removes the onboarding screen.

app/src/main/res/layout/activity_home.xml

@@ -7,7 +7,6 @@
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:orientation="vertical"
-    android:id="@+id/rootContainer"
     tools:context=".HomeActivity">
 
     <ViewStub