Fix Modal when the Activity is paused or resumed

Summary:
When the activity hosting a Modal goes away, we should dismiss the dialog from the stack and then reconstitute it when the activity comes back.  This means that if an activity is paused because another activity is placed on top of it but our ui operation was delayed, it will not blow up finding no window since it is gone.

Also fixes a place where we should remove a listener for lifecycle events which we were not doing.

Reviewed By: halfjuice

Differential Revision: D3357286

fbshipit-source-id: c5c6dd8e5ef299762ed9aa15a6910ce9c0b111dc

ReactAndroid/src/main/java/com/facebook/react/views/modal/ReactModalHostManager.java

@@ -62,7 +62,7 @@ public class ReactModalHostManager extends ViewGroupManager<ReactModalHostView>
   @Override
   public void onDropViewInstance(ReactModalHostView view) {
     super.onDropViewInstance(view);
-    view.dismiss();
+    view.onDropInstance();
   }
 
   @ReactProp(name = "animationType")

ReactAndroid/src/main/java/com/facebook/react/views/modal/ReactModalHostView.java

@@ -109,7 +109,12 @@ public class ReactModalHostView extends ViewGroup implements LifecycleEventListe
     // Those will be handled by the mHostView which lives in the dialog
   }
 
-  public void dismiss() {
+  public void onDropInstance() {
+    ((ReactContext) getContext()).removeLifecycleEventListener(this);
+    dismiss();
+  }
+
+  private void dismiss() {
     if (mDialog != null) {
       mDialog.dismiss();
       mDialog = null;
@@ -140,18 +145,20 @@ public class ReactModalHostView extends ViewGroup implements LifecycleEventListe
 
   @Override
   public void onHostResume() {
-    // do nothing
+    // We show the dialog again when the host resumes
+    showOrUpdate();
   }
 
   @Override
   public void onHostPause() {
-    // do nothing
+    // We dismiss the dialog and reconstitute it onHostResume
+    dismiss();
   }
 
   @Override
   public void onHostDestroy() {
-    // Dismiss the dialog if it is present
-    dismiss();
+    // Drop the instance if the host is destroyed which will dismiss the dialog
+    onDropInstance();
   }
 
   @VisibleForTesting