Finish AccessibilityInfo implementation

Summary:
This PR is based on files ericvicenti gave me. Specifically, he gave me:
  - AccessibilityInfo.android.js
  - AccessibilityInfo.ios.js
  - AccessibilityInfoModule.java

Before this change, only a native iOS implementation of AccessibilityInfo existed. This change includes:
  - A native Android implementation of AccessibilityInfo.
  - JavaScript wrappers for the AccessibilityInfo module for both iOS and Android.
  - UIExplorer changes to illustrate how to use AccessibilityInfo on iOS and Android.
  - Documentation for the AccessibilityInfo APIs.

**Test plan (required)**

Tested the UIExplorer AccessibilityInfo example on iOS and Android with the screen reader both enabled and disabled.

Adam Comella
Microsoft Corp.
Closes https://github.com/facebook/react-native/pull/12273

Reviewed By: mkonicek

Differential Revision: D4527224

Pulled By: ericvicenti

fbshipit-source-id: d04638465ccbdbb35ecfc9504daaeb8e33aab57a

ReactAndroid/src/main/java/com/facebook/react/modules/accessibilityinfo/AccessibilityInfoModule.java

@@ -0,0 +1,98 @@
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+package com.facebook.react.modules.accessibilityinfo;
+
+import javax.annotation.Nullable;
+
+import android.annotation.TargetApi;
+import android.content.Context;
+import android.os.Build;
+import android.view.accessibility.AccessibilityManager;
+
+import com.facebook.react.bridge.Callback;
+import com.facebook.react.bridge.LifecycleEventListener;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.bridge.ReactContextBaseJavaModule;
+import com.facebook.react.bridge.ReactMethod;
+import com.facebook.react.module.annotations.ReactModule;
+import com.facebook.react.modules.core.DeviceEventManagerModule;
+
+/**
+ * Module that monitors and provides information about the state of Touch Exploration service
+ * on the device. For API >= 19.
+ */
+@ReactModule(name = "AccessibilityInfo")
+public class AccessibilityInfoModule extends ReactContextBaseJavaModule
+        implements LifecycleEventListener {
+
+    @TargetApi(19)
+    private class ReactTouchExplorationStateChangeListener
+            implements AccessibilityManager.TouchExplorationStateChangeListener {
+
+        @Override
+        public void onTouchExplorationStateChanged(boolean enabled) {
+            updateAndSendChangeEvent(enabled);
+        }
+    }
+
+    private @Nullable AccessibilityManager mAccessibilityManager;
+    private @Nullable ReactTouchExplorationStateChangeListener mTouchExplorationStateChangeListener;
+    private boolean mEnabled = false;
+
+    private static final String EVENT_NAME = "touchExplorationDidChange";
+
+    public AccessibilityInfoModule(ReactApplicationContext context) {
+        super(context);
+        mAccessibilityManager = (AccessibilityManager) getReactApplicationContext()
+                .getSystemService(Context.ACCESSIBILITY_SERVICE);
+        mEnabled = mAccessibilityManager.isTouchExplorationEnabled();
+        if (Build.VERSION.SDK_INT >= 19) {
+            mTouchExplorationStateChangeListener = new ReactTouchExplorationStateChangeListener();
+        }
+    }
+
+    @Override
+    public String getName() {
+        return "AccessibilityInfo";
+    }
+
+    @ReactMethod
+    public void isTouchExplorationEnabled(Callback successCallback) {
+        successCallback.invoke(mEnabled);
+    }
+
+    private void updateAndSendChangeEvent(boolean enabled) {
+        if (mEnabled != enabled) {
+            mEnabled = enabled;
+            getReactApplicationContext().getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)
+                    .emit(EVENT_NAME, mEnabled);
+        }
+    }
+
+    @Override
+    public void onHostResume() {
+        if (Build.VERSION.SDK_INT >= 19) {
+            mAccessibilityManager.addTouchExplorationStateChangeListener(
+                    mTouchExplorationStateChangeListener);
+        }
+        updateAndSendChangeEvent(mAccessibilityManager.isTouchExplorationEnabled());
+    }
+
+    @Override
+    public void onHostPause() {
+        if (Build.VERSION.SDK_INT >= 19) {
+            mAccessibilityManager.removeTouchExplorationStateChangeListener(
+                    mTouchExplorationStateChangeListener);
+        }
+    }
+
+    @Override
+    public void initialize() {
+        getReactApplicationContext().addLifecycleEventListener(this);
+        updateAndSendChangeEvent(mAccessibilityManager.isTouchExplorationEnabled());
+    }
+
+    @Override
+    public void onHostDestroy() {
+    }
+}

ReactAndroid/src/main/java/com/facebook/react/modules/accessibilityinfo/BUCK

@@ -0,0 +1,22 @@
+include_defs("//ReactAndroid/DEFS")
+
+android_library(
+    name = "accessibilityinfo",
+    srcs = glob(["**/*.java"]),
+    visibility = [
+        "PUBLIC",
+    ],
+    deps = [
+        react_native_dep("libraries/fbcore/src/main/java/com/facebook/common/logging:logging"),
+        react_native_dep("third-party/java/infer-annotations:infer-annotations"),
+        react_native_dep("third-party/java/jsr-305:jsr-305"),
+        react_native_target("java/com/facebook/react/bridge:bridge"),
+        react_native_target("java/com/facebook/react/common:common"),
+        react_native_target("java/com/facebook/react/module/annotations:annotations"),
+        react_native_target("java/com/facebook/react/modules/core:core"),
+    ],
+)
+
+project_config(
+    src_target = ":accessibilityinfo",
+)

ReactAndroid/src/main/java/com/facebook/react/shell/BUCK

@@ -19,6 +19,7 @@ android_library(
         react_native_target("java/com/facebook/react/devsupport:devsupport"),
         react_native_target("java/com/facebook/react/flat:flat"),
         react_native_target("java/com/facebook/react/module/model:model"),
+        react_native_target("java/com/facebook/react/modules/accessibilityinfo:accessibilityinfo"),
         react_native_target("java/com/facebook/react/modules/appstate:appstate"),
         react_native_target("java/com/facebook/react/modules/camera:camera"),
         react_native_target("java/com/facebook/react/modules/clipboard:clipboard"),

ReactAndroid/src/main/java/com/facebook/react/shell/MainReactPackage.java

@@ -36,6 +36,7 @@ import com.facebook.react.flat.RCTViewManager;
 import com.facebook.react.flat.RCTViewPagerManager;
 import com.facebook.react.flat.RCTVirtualTextManager;
 import com.facebook.react.module.model.ReactModuleInfoProvider;
+import com.facebook.react.modules.accessibilityinfo.AccessibilityInfoModule;
 import com.facebook.react.modules.appstate.AppStateModule;
 import com.facebook.react.modules.camera.CameraRollManager;
 import com.facebook.react.modules.camera.ImageEditingManager;
@@ -102,6 +103,12 @@ public class MainReactPackage extends LazyReactPackage {
   @Override
   public List<ModuleSpec> getNativeModules(final ReactApplicationContext context) {
     return Arrays.asList(
+      new ModuleSpec(AccessibilityInfoModule.class, new Provider<NativeModule>() {
+        @Override
+        public NativeModule get() {
+          return new AccessibilityInfoModule(context);
+        }
+      }),
       new ModuleSpec(AppStateModule.class, new Provider<NativeModule>() {
         @Override
         public NativeModule get() {