Add new quickstep test for many tasks open at once.

This test is needed for testing overview-grid-related functionality.
- Opening non-focused tasks
- Dismissing a non-focused task from the grid
- Grid rows rebalancing after dismissal, which only happens when enough
apps are open to be off-screen.
- Grid tasks do not scroll after dismissal.

Test: TaplTestsQuickstep.java
Bug: 197630182
Change-Id: Ic907db4643cdc2eb9e4610dab917347e234e470c

tests/src/com/android/launcher3/testcomponent/OtherBaseTestingActivity.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2018 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.launcher3.testcomponent;
+
+/**
+ * Extension of BaseTestingActivity to help test many activities open at once.
+ */
+public class OtherBaseTestingActivity extends BaseTestingActivity {}