Add magnification switch shortcut dialog.

* show dialog when triple-tap users want to use magnify window mode

Bug: 146473544
Test: manual
Change-Id: I6915c165e8da59c6ec7557147192c7a1e9e19cf3

res/layout/accessibility_edit_magnification_shortcut.xml

@@ -0,0 +1,55 @@
+<?xml version="1.0" encoding="utf-8"?><!--
+  Copyright (C) 2020 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
+  -->
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/container_layout"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:scrollbarStyle="outsideOverlay">
+
+    <LinearLayout
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:orientation="vertical"
+        android:padding="24dp">
+
+        <TextView
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:text="@string/accessibility_magnification_switch_shortcut_message"
+            android:textAppearance="?android:attr/textAppearanceListItemSecondary"
+            android:textColor="?android:attr/textColorSecondary"
+            android:layout_marginBottom="24dp"/>
+
+        <LinearLayout
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:orientation="vertical">
+
+            <Button
+                android:id="@+id/switch_shortcut_positive_button"
+                style="@style/AccessibilityDialogButton"
+                android:gravity="center|end"
+                android:text="@string/accessibility_magnification_switch_shortcut_positive_button"/>
+
+            <Button
+                android:id="@+id/switch_shortcut_negative_button"
+                style="@style/AccessibilityDialogButton"
+                android:gravity="center|end"
+                android:text="@string/accessibility_magnification_switch_shortcut_negative_button"/>
+
+        </LinearLayout>
+    </LinearLayout>
+</ScrollView>