add onStart hook which places flutter in an inactive state (#5177)

shell/platform/android/io/flutter/app/FlutterActivity.java

@@ -81,6 +81,12 @@ public class FlutterActivity extends Activity implements FlutterView.Provider, P
         eventDelegate.onCreate(savedInstanceState);
     }
 
+    @Override
+    protected void onStart() {
+        super.onStart();
+        eventDelegate.onStart();
+    }
+
     @Override
     protected void onResume() {
         super.onResume();

shell/platform/android/io/flutter/app/FlutterActivityDelegate.java

@@ -206,6 +206,13 @@ public final class FlutterActivityDelegate
         }
     }
 
+    @Override
+    public void onStart() {
+        if (flutterView != null) {
+            flutterView.onStart();
+        }
+    }
+
     @Override
     public void onResume() {
         Application app = (Application) activity.getApplicationContext();

shell/platform/android/io/flutter/app/FlutterActivityEvents.java

@@ -39,6 +39,11 @@ public interface FlutterActivityEvents
      */
     void onPause();
 
+    /**
+     * @see android.app.Activity#onStart()
+     */
+    void onStart();
+
     /**
      * @see android.app.Activity#onResume()
      */

shell/platform/android/io/flutter/view/FlutterView.java

@@ -266,6 +266,10 @@ public class FlutterView extends SurfaceView
         mActivityLifecycleListeners.add(listener);
     }
 
+    public void onStart() {
+        mFlutterLifecycleChannel.send("AppLifecycleState.inactive");
+    }
+
     public void onPause() {
         mFlutterLifecycleChannel.send("AppLifecycleState.inactive");
     }