Expose initialAppState constant from Android native AppState module (f…

…acebook#19935)

Summary:
This PR addresses TODO left in _AppState.js_

The goal is to align AppState module implementation between iOS and Android. iOS native module exposes _initialAppState_ constant that AppState.js relies on, while Android doesn't expose that constant and js implementation uses a fallback. This PR aims to remove a need for a fallback
Pull Request resolved: facebook#19935

Reviewed By: hramos

Differential Revision: D13774044

Pulled By: ejanzer

fbshipit-source-id: 05d27e702cb9aeedf14293158bfd50004df4726b

ReactAndroid/src/main/java/com/facebook/react/modules/appstate/AppStateModule.java

@@ -14,9 +14,13 @@
 import com.facebook.react.bridge.ReactContextBaseJavaModule;
 import com.facebook.react.bridge.ReactMethod;
 import com.facebook.react.bridge.WritableMap;
+import com.facebook.react.common.LifecycleState;
 import com.facebook.react.module.annotations.ReactModule;
 import com.facebook.react.modules.core.DeviceEventManagerModule.RCTDeviceEventEmitter;
 
+import java.util.HashMap;
+import java.util.Map;
+
 @ReactModule(name = AppStateModule.NAME)
 public class AppStateModule extends ReactContextBaseJavaModule
         implements LifecycleEventListener {
@@ -26,10 +30,15 @@ public class AppStateModule extends ReactContextBaseJavaModule
   public static final String APP_STATE_ACTIVE = "active";
   public static final String APP_STATE_BACKGROUND = "background";
 
-  private String mAppState = "uninitialized";
+  private static final String INITIAL_STATE = "initialAppState";
+
+  private String mAppState;
 
   public AppStateModule(ReactApplicationContext reactContext) {
     super(reactContext);
+    reactContext.addLifecycleEventListener(this);
+    mAppState = (reactContext.getLifecycleState() == LifecycleState.RESUMED ?
+            APP_STATE_ACTIVE : APP_STATE_BACKGROUND);
   }
 
   @Override
@@ -38,8 +47,10 @@ public String getName() {
   }
 
   @Override
-  public void initialize() {
-    getReactApplicationContext().addLifecycleEventListener(this);
+  public Map<String, Object> getConstants() {
+    HashMap<String, Object> constants = new HashMap<>();
+    constants.put(INITIAL_STATE, mAppState);
+    return constants;
   }
 
   @ReactMethod