For #12201 - forced callbacks to be on the main thread (#12543)

app/src/main/java/org/mozilla/fenix/sync/SyncedTabsLayout.kt

@@ -10,6 +10,10 @@ import android.view.View
 import android.widget.FrameLayout
 import androidx.recyclerview.widget.LinearLayoutManager
 import kotlinx.android.synthetic.main.component_sync_tabs.view.*
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.cancel
 import mozilla.components.browser.storage.sync.SyncedDeviceTabs
 import mozilla.components.feature.syncedtabs.view.SyncedTabsView
 import org.mozilla.fenix.R
@@ -23,6 +27,7 @@ class SyncedTabsLayout @JvmOverloads constructor(
     override var listener: SyncedTabsView.Listener? = null
 
     private val adapter = SyncedTabsAdapter { listener?.onTabClicked(it) }
+    private val coroutineScope = CoroutineScope(Dispatchers.Main)
 
     init {
         inflate(getContext(), R.layout.component_sync_tabs, this)
@@ -34,6 +39,7 @@ class SyncedTabsLayout @JvmOverloads constructor(
     }
 
     override fun onError(error: SyncedTabsView.ErrorType) {
+        coroutineScope.launch {
             // We may still be displaying a "loading" spinner, hide it.
             stopLoading()
 
@@ -52,8 +58,10 @@ class SyncedTabsLayout @JvmOverloads constructor(
 
             synced_tabs_pull_to_refresh.isEnabled = pullToRefreshEnableState(error)
         }
+    }
 
     override fun displaySyncedTabs(syncedTabs: List<SyncedDeviceTabs>) {
+        coroutineScope.launch {
             synced_tabs_list.visibility = View.VISIBLE
             sync_tabs_status.visibility = View.GONE
 
@@ -71,6 +79,7 @@ class SyncedTabsLayout @JvmOverloads constructor(
 
             adapter.submitList(allDeviceTabs)
         }
+    }
 
     override fun startLoading() {
         synced_tabs_list.visibility = View.VISIBLE
@@ -83,6 +92,11 @@ class SyncedTabsLayout @JvmOverloads constructor(
         synced_tabs_pull_to_refresh.isRefreshing = false
     }
 
+    override fun onDetachedFromWindow() {
+        super.onDetachedFromWindow()
+        coroutineScope.cancel()
+    }
+
     companion object {
         internal fun pullToRefreshEnableState(error: SyncedTabsView.ErrorType) = when (error) {
             // Disable "pull-to-refresh" when we clearly can't sync tabs, and user needs to take an