Use synchronize instead of Assert.isMainThread

DemoModeController tried to make sure adding callbacks always happened
on the main thread. But it's breaking some tests if it somehow gets
instantiated (lazily, by Dagger) on a background thread.

It should be fine to just use a couple of locks and call it a day, but
eventually it'd be better to fix that dagger problem...

Test: atest SystemUITests
Fixes: 170122983
Change-Id: Ieff52b268aec4194e932823353c739c1e0641acc

packages/SystemUI/src/com/android/systemui/demomode/DemoModeController.kt

@@ -85,8 +85,6 @@ class DemoModeController constructor(
     }
 
     override fun addCallback(listener: DemoMode) {
-        Assert.isMainThread()
-
         // Register this listener for its commands
         val commands = listener.demoCommands()
 
@@ -99,20 +97,23 @@ class DemoModeController constructor(
             receiverMap[command]!!.add(listener)
         }
 
-        receivers.add(listener)
+        synchronized(this) {
+            receivers.add(listener)
+        }
+
         if (isInDemoMode) {
             listener.onDemoModeStarted()
         }
     }
 
     override fun removeCallback(listener: DemoMode) {
-        Assert.isMainThread()
+        synchronized(this) {
+            listener.demoCommands().forEach { command ->
+                receiverMap[command]!!.remove(listener)
+            }
 
-        listener.demoCommands().forEach { command ->
-            receiverMap[command]!!.remove(listener)
+            receivers.remove(listener)
         }
-
-        receivers.remove(listener)
     }
 
     private fun setIsDemoModeAllowed(enabled: Boolean) {
@@ -125,7 +126,13 @@ class DemoModeController constructor(
     private fun enterDemoMode() {
         isInDemoMode = true
         Assert.isMainThread()
-        receivers.forEach { r ->
+
+        val copy: List<DemoModeCommandReceiver>
+        synchronized(this) {
+            copy = receivers.toList()
+        }
+
+        copy.forEach { r ->
             r.onDemoModeStarted()
         }
     }
@@ -133,7 +140,13 @@ class DemoModeController constructor(
     private fun exitDemoMode() {
         isInDemoMode = false
         Assert.isMainThread()
-        receivers.forEach { r ->
+
+        val copy: List<DemoModeCommandReceiver>
+        synchronized(this) {
+            copy = receivers.toList()
+        }
+
+        copy.forEach { r ->
             r.onDemoModeFinished()
         }
     }
@@ -168,7 +181,11 @@ class DemoModeController constructor(
         pw.println("  isInDemoMode=$isInDemoMode")
         pw.println("  isDemoModeAllowed=$isAvailable")
         pw.print("  receivers=[")
-        receivers.forEach { recv ->
+        val copy: List<DemoModeCommandReceiver>
+        synchronized(this) {
+            copy = receivers.toList()
+        }
+        copy.forEach { recv ->
             pw.print(" ${recv.javaClass.simpleName}")
         }
         pw.println(" ]")