Opening and closing Synced Tabs crashes

[jonalmeida]

Steps to reproduce

1. Open and close the Synced Tabs view quickly before.

Expected behavior

• Don't crash.

Actual behavior

• 💥

Device information

• Android device: Android 10, Pixel 4
• Reference Browser version: Nightly, 2020-06-02

25cee985-b1d9-4180-8123-24a986715394
android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
 * Socorro: https://crash-stats.mozilla.org/report/index/bp-b162d95d-b87d-419f-8f35-e91ce0200602
 * Sentry: <No URL>
----
android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
	at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:8372)
	at android.view.ViewRootImpl.focusableViewAvailable(ViewRootImpl.java:4273)
	at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:940)
	at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:940)
	at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:940)
	at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:940)
	at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:940)
	at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:940)
	at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:940)
	at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:940)
	at android.view.ViewGroup.focusableViewAvailable(ViewGroup.java:940)
	at android.view.View.setFlags(View.java:15732)
	at android.view.View.setVisibility(View.java:11372)
	at org.mozilla.reference.browser.tabs.synced.SyncedTabsLayout.startLoading(SyncedTabsLayout.kt:72)
	at mozilla.components.feature.syncedtabs.controller.DefaultController.refreshSyncedTabs(DefaultController.kt:31)
	at mozilla.components.feature.syncedtabs.presenter.DefaultPresenter$SyncedTabsAccountObserver.onAuthenticated(DefaultPresenter.kt:92)
	at mozilla.components.service.fxa.manager.FxaAccountManager$postAuthenticated$3.invoke(FxaAccountManager.kt:960)
	at mozilla.components.service.fxa.manager.FxaAccountManager$postAuthenticated$3.invoke(FxaAccountManager.kt:150)
	at mozilla.components.support.base.observer.ObserverRegistry.notifyObservers(ObserverRegistry.kt:137)
	at mozilla.components.service.fxa.manager.FxaAccountManager.notifyObservers(Unknown Source:7)
	at mozilla.components.service.fxa.manager.FxaAccountManager.postAuthenticated(FxaAccountManager.kt:960)
	at mozilla.components.service.fxa.manager.FxaAccountManager$postAuthenticated$1.invokeSuspend(Unknown Source:12)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:56)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.lang.Thread.run(Thread.java:919)