[fenix] Close https://github.com/mozilla-mobile/fenix/issues/25919: Move UpdateFirstFrameDrawn to RecyclerView.onLayoutCompleted

As part of a preventitive measure for home page regression loading, we
fixed the UpdateFirstFrameDrawn call to happen after the first layout in
the main RecyclerView is completed. In addition, we also make pocket
aware of this flag so that it renders itself after the first layout.

This helps prioritize current & future features that are visible first
to render before those that are off screen.

Co-authored-by: Arturo Mejia <arturomejiamarmol@gmail.com>

app/src/main/java/org/mozilla/fenix/home/HomeFragment.kt

@@ -26,7 +26,6 @@ import androidx.constraintlayout.widget.ConstraintSet.PARENT_ID
 import androidx.constraintlayout.widget.ConstraintSet.TOP
 import androidx.coordinatorlayout.widget.CoordinatorLayout
 import androidx.core.content.ContextCompat
-import androidx.core.view.doOnPreDraw
 import androidx.core.view.isVisible
 import androidx.core.view.updateLayoutParams
 import androidx.fragment.app.Fragment
@@ -398,10 +397,6 @@ class HomeFragment : Fragment() {
 
         FxNimbus.features.homescreen.recordExposure()
 
-        binding.root.doOnPreDraw {
-            requireComponents.appStore.dispatch(AppAction.UpdateFirstFrameDrawn(drawn = true))
-        }
-
         // DO NOT MOVE ANYTHING BELOW THIS addMarker CALL!
         requireComponents.core.engine.profiler?.addMarker(
             MarkersFragmentLifecycleCallbacks.MARKER_NAME, profilerStartTime, "HomeFragment.onCreateView",

app/src/main/java/org/mozilla/fenix/home/sessioncontrol/SessionControlView.kt

@@ -12,6 +12,7 @@ import androidx.recyclerview.widget.RecyclerView
 import mozilla.components.feature.tab.collections.TabCollection
 import mozilla.components.feature.top.sites.TopSite
 import mozilla.components.service.pocket.PocketStory
+import org.mozilla.fenix.components.appstate.AppAction
 import org.mozilla.fenix.components.appstate.AppState
 import org.mozilla.fenix.ext.components
 import org.mozilla.fenix.ext.settings
@@ -41,7 +42,8 @@ internal fun normalModeAdapterItems(
     showRecentTab: Boolean,
     showRecentSyncedTab: Boolean,
     recentVisits: List<RecentlyVisitedItem>,
-    pocketStories: List<PocketStory>
+    pocketStories: List<PocketStory>,
+    firstFrameDrawn: Boolean = false,
 ): List<AdapterItem> {
     val items = mutableListOf<AdapterItem>()
     var shouldShowCustomizeHome = false
@@ -86,7 +88,11 @@ internal fun normalModeAdapterItems(
         showCollections(collections, expandedCollections, items)
     }
 
-    if (settings.showPocketRecommendationsFeature && pocketStories.isNotEmpty()) {
+    // When Pocket is enabled and the initial layout of the app is done, then we can add these items
+    // to render to the home screen.
+    // This is only useful while we have a RecyclerView + Compose implementation. We can remove this
+    // when we switch to a Compose-only home screen.
+    if (firstFrameDrawn && settings.showPocketRecommendationsFeature && pocketStories.isNotEmpty()) {
         shouldShowCustomizeHome = true
         items.add(AdapterItem.PocketStoriesItem)
         items.add(AdapterItem.PocketCategoriesItem)
@@ -166,7 +172,8 @@ private fun AppState.toAdapterList(settings: Settings): List<AdapterItem> = when
         shouldShowRecentTabs(settings),
         shouldShowRecentSyncedTabs(settings),
         recentHistory,
-        pocketStories
+        pocketStories,
+        firstFrameDrawn
     )
     is Mode.Private -> privateModeAdapterItems()
     is Mode.Onboarding -> onboardingAdapterItems(mode.state)
@@ -207,6 +214,15 @@ class SessionControlView(
                         ).showSyncCFR()
                         context.settings().showSyncCFR = false
                     }
+
+                    // We want some parts of the home screen UI to be rendered first if they are
+                    // the most prominent parts of the visible part of the screen.
+                    // For this reason, we wait for the home screen recycler view to finish it's
+                    // layout and post an update for when it's best for non-visible parts of the
+                    // home screen to render itself.
+                    containerView.context.components.appStore.dispatch(
+                        AppAction.UpdateFirstFrameDrawn(true)
+                    )
                 }
             }
         }

app/src/test/java/org/mozilla/fenix/home/sessioncontrol/SessionControlViewTest.kt

@@ -217,7 +217,8 @@ class SessionControlViewTest {
             false,
             showRecentSyncedTab = false,
             historyMetadata,
-            pocketStories
+            pocketStories,
+            true
         )
 
         assertTrue(results[0] is AdapterItem.TopPlaceholderItem)
@@ -225,6 +226,25 @@ class SessionControlViewTest {
         assertTrue(results[2] is AdapterItem.PocketCategoriesItem)
         assertTrue(results[3] is AdapterItem.PocketRecommendationsFooterItem)
         assertTrue(results[4] is AdapterItem.CustomizeHomeButton)
+
+        // When the first frame has not yet drawn don't add pocket.
+        val results2 = normalModeAdapterItems(
+            settings,
+            topSites,
+            collections,
+            expandedCollections,
+            recentBookmarks,
+            false,
+            null,
+            false,
+            showRecentSyncedTab = false,
+            historyMetadata,
+            pocketStories,
+            false
+        )
+
+        assertTrue(results2[0] is AdapterItem.TopPlaceholderItem)
+        assertTrue(results2[1] is AdapterItem.BottomSpacer)
     }
 
     @Test