Use bg thread for BroadcastDispatcher registering

There is no need for the broadcastdispatcher to register in the main
thread. Moving to the bg thread reduces the chance of our main thread
being busy when many classes subscribe in a short period of time.

Test: manual (logs show BroadcastDispatcher is receiving broadcasts)
Test: atest UserBroadcastDispatcherTest
Fixes: 151684085
Change-Id: Iac6fd9e3b9f7bed3879620b4f262cc68f8ffdcd3

packages/SystemUI/src/com/android/systemui/broadcast/BroadcastDispatcher.kt

@@ -166,7 +166,7 @@ open class BroadcastDispatcher @Inject constructor (
 
     @VisibleForTesting
     protected open fun createUBRForUser(userId: Int) =
-            UserBroadcastDispatcher(context, userId, mainHandler, bgLooper)
+            UserBroadcastDispatcher(context, userId, bgLooper)
 
     override fun dump(fd: FileDescriptor, pw: PrintWriter, args: Array<out String>) {
         pw.println("Broadcast dispatcher:")

packages/SystemUI/src/com/android/systemui/broadcast/UserBroadcastDispatcher.kt

@@ -27,7 +27,6 @@ import android.os.UserHandle
 import android.util.ArrayMap
 import android.util.ArraySet
 import android.util.Log
-import androidx.annotation.MainThread
 import androidx.annotation.VisibleForTesting
 import com.android.internal.util.Preconditions
 import com.android.systemui.Dumpable
@@ -46,11 +45,13 @@ private const val DEBUG = false
  *
  * Created by [BroadcastDispatcher] as needed by users. The value of [userId] can be
  * [UserHandle.USER_ALL].
+ *
+ * Each instance of this class will register itself exactly once with [Context]. Updates to the
+ * [IntentFilter] will be done in the background thread.
  */
 class UserBroadcastDispatcher(
     private val context: Context,
     private val userId: Int,
-    private val mainHandler: Handler,
     private val bgLooper: Looper
 ) : BroadcastReceiver(), Dumpable {
 
@@ -168,7 +169,7 @@ class UserBroadcastDispatcher(
     // Only call this from a BG thread
     private fun createFilterAndRegisterReceiverBG() {
         val intentFilter = createFilter()
-        mainHandler.post(RegisterReceiverRunnable(intentFilter))
+        bgHandler.post(RegisterReceiverRunnable(intentFilter))
     }
 
     override fun dump(fd: FileDescriptor, pw: PrintWriter, args: Array<out String>) {
@@ -207,10 +208,7 @@ class UserBroadcastDispatcher(
 
         /*
          * Registers and unregisters the BroadcastReceiver
-         *
-         * Must be called from Main Thread
          */
-        @MainThread
         override fun run() {
             if (registered.get()) {
                 context.unregisterReceiver(this@UserBroadcastDispatcher)

packages/SystemUI/tests/src/com/android/systemui/broadcast/UserBroadcastDispatcherTest.kt

@@ -91,7 +91,7 @@ class UserBroadcastDispatcherTest : SysuiTestCase() {
         fakeExecutor = FakeExecutor(FakeSystemClock())
 
         userBroadcastDispatcher = UserBroadcastDispatcher(
-                mockContext, USER_ID, handler, testableLooper.looper)
+                mockContext, USER_ID, testableLooper.looper)
         userBroadcastDispatcher.pendingResult = mPendingResult
     }