Use FakeTimer in test to avoid flakiness.

**Root cause**
ScreenFlashNotificationColorDialogFragment creates Timer which spawns
unmanageable threads for tests. Also, the test itself uses Thread.sleep
which makes it non-destermistic.

Bug: 279082331
Test: atest ScreenFlashNotificationColorDialogFragmentTest --iteration
20

Change-Id: Id49c8d402a0578f8297ca12fe49da304c7a988d8

tests/robotests/src/com/android/settings/testutils/FakeTimer.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.testutils;
+
+import java.util.PriorityQueue;
+import java.util.Timer;
+import java.util.TimerTask;
+
+/**
+ * A fake {@link Timer} that doesn't create a TimerThread which is hard to manage in test.
+ */
+public class FakeTimer extends Timer {
+    private final PriorityQueue<ScheduledTimerTask> mQueue = new PriorityQueue<>();
+
+    public FakeTimer() {
+    }
+
+    @Override
+    public void cancel() {
+        mQueue.clear();
+    }
+
+    @Override
+    public void schedule(TimerTask task, long delay) {
+        mQueue.offer(new ScheduledTimerTask(System.currentTimeMillis() + delay, task));
+    }
+
+    /**
+     * Runs the first task in the queue if there's any.
+     */
+    public void runOneTask() {
+        if (mQueue.size() > 0) {
+            mQueue.poll().mTask.run();
+        }
+    }
+
+    /**
+     * Runs all the queued tasks in order.
+     */
+    public void runAllTasks() {
+        while (mQueue.size() > 0) {
+            mQueue.poll().mTask.run();
+        }
+    }
+
+    /**
+     * Returns number of pending tasks in the timer
+     */
+    public int numOfPendingTasks() {
+        return mQueue.size();
+    }
+
+    private static class ScheduledTimerTask implements Comparable<ScheduledTimerTask> {
+        final long mTimeToRunInMillisSeconds;
+        final TimerTask mTask;
+
+        ScheduledTimerTask(long timeToRunInMilliSeconds, TimerTask task) {
+            this.mTimeToRunInMillisSeconds = timeToRunInMilliSeconds;
+            this.mTask = task;
+        }
+
+        @Override
+        public int compareTo(ScheduledTimerTask other) {
+            return Long.compare(this.mTimeToRunInMillisSeconds, other.mTimeToRunInMillisSeconds);
+        }
+    }
+}