Fix 4827 - Use ktx doOnPreDraw() to restore HomeFragment's layout

The previous solution would result in a crash because the passed in
viewTreeObserver that would trigger onPreDraw would be invalid.
The proposed solution is simpler and ensures we'll always use the right
viewTreeObserver.

`FragmentPreDrawManager` is general enough that can be used by other Fragments
also, so I've added it to the `utils` package.

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

@@ -81,6 +81,7 @@ import org.mozilla.fenix.mvi.getManagedEmitter
 import org.mozilla.fenix.onboarding.FenixOnboarding
 import org.mozilla.fenix.settings.SupportUtils
 import org.mozilla.fenix.share.ShareTab
+import org.mozilla.fenix.utils.FragmentPreDrawManager
 import org.mozilla.fenix.utils.allowUndo
 
 @SuppressWarnings("TooManyFunctions", "LargeClass")
@@ -182,20 +183,6 @@ class HomeFragment : Fragment(), AccountObserver {
         val activity = activity as HomeActivity
         activity.themeManager.applyStatusBarTheme(activity)
 
-        postponeEnterTransition()
-        TransitionPreDrawListener(
-            fragment = this,
-            viewTreeObserver = sessionControlComponent.view.viewTreeObserver,
-            restoreLayoutState = {
-                val homeViewModel: HomeScreenViewModel by activityViewModels()
-                homeViewModel.layoutManagerState?.also { parcelable ->
-                    sessionControlComponent.view.layoutManager?.onRestoreInstanceState(parcelable)
-                }
-                homeLayout?.progress = homeViewModel.motionLayoutProgress
-                homeViewModel.layoutManagerState = null
-            }
-        )
-
         return view
     }
 
@@ -203,6 +190,15 @@ class HomeFragment : Fragment(), AccountObserver {
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)
 
+        FragmentPreDrawManager(this).execute {
+            val homeViewModel: HomeScreenViewModel by activityViewModels()
+            homeViewModel.layoutManagerState?.also { parcelable ->
+                sessionControlComponent.view.layoutManager?.onRestoreInstanceState(parcelable)
+            }
+            homeLayout?.progress = homeViewModel.motionLayoutProgress
+            homeViewModel.layoutManagerState = null
+        }
+
         setupHomeMenu()
 
         viewLifecycleOwner.lifecycleScope.launch(Dispatchers.IO) {

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

@@ -1,52 +0,0 @@
-/* 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.home
-
-import android.view.ViewTreeObserver
-import androidx.fragment.app.Fragment
-import androidx.lifecycle.Lifecycle
-import androidx.lifecycle.LifecycleObserver
-import androidx.lifecycle.OnLifecycleEvent
-import androidx.lifecycle.lifecycleScope
-import kotlinx.coroutines.delay
-import kotlinx.coroutines.launch
-
-class TransitionPreDrawListener(
-    private val fragment: Fragment,
-    private val viewTreeObserver: ViewTreeObserver,
-    private val restoreLayoutState: () -> Unit
-) : ViewTreeObserver.OnPreDrawListener, LifecycleObserver {
-
-    init {
-        fragment.viewLifecycleOwner.lifecycle.addObserver(this)
-    }
-
-    @OnLifecycleEvent(Lifecycle.Event.ON_CREATE)
-    fun onCreateView() {
-        viewTreeObserver.addOnPreDrawListener(this)
-    }
-
-    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
-    fun onDestroyView() {
-        viewTreeObserver.removeOnPreDrawListener(this)
-    }
-
-    override fun onPreDraw(): Boolean {
-        if (fragment.view != null) {
-            fragment.viewLifecycleOwner.lifecycleScope.launch {
-                delay(ANIM_SCROLL_DELAY)
-                restoreLayoutState()
-                fragment.startPostponedEnterTransition()
-            }.invokeOnCompletion {
-                viewTreeObserver.removeOnPreDrawListener(this)
-            }
-        }
-        return true
-    }
-
-    companion object {
-        private const val ANIM_SCROLL_DELAY = 100L
-    }
-}

app/src/main/java/org/mozilla/fenix/utils/FragmentPreDrawManager.kt

@@ -0,0 +1,36 @@
+/* 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.utils
+
+import androidx.core.view.doOnPreDraw
+import androidx.fragment.app.Fragment
+import androidx.lifecycle.lifecycleScope
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
+
+/**
+ * Helper class that allows executing code immediately before [Fragment]s View being drawn.
+ */
+class FragmentPreDrawManager(
+    private val fragment: Fragment
+) {
+    init {
+        fragment.postponeEnterTransition()
+    }
+
+    fun execute(code: () -> Unit) {
+        fragment.view?.doOnPreDraw {
+            fragment.viewLifecycleOwner.lifecycleScope.launch {
+                delay(ANIM_SCROLL_DELAY)
+                code()
+                fragment.startPostponedEnterTransition()
+            }
+        }
+    }
+
+    companion object {
+        private const val ANIM_SCROLL_DELAY = 100L
+    }
+}