Fix not processing Visibility events on parent LithoView when it has …

…transient child LithoViews

Summary:
We process our visibility evens in 2 cases: `Extension.afterMount` or `Extension.onVisibleBoundsChanged`. In both cases if the view is in transient state, we skip processing until it's not. We rely on `setHasTransientState(false)` to be called eventually to return the view back to non transient state. But in realty `setHasTransientState(true)` is not the only was to make a view transient. It transitively becomes transient, when any of its children becomes transient. This was the case in the issue that uncovered this bug — child LithoViews sometimes were in transient state in `afterMount` or `onVisibleBoundsChanged`, resulting in parent LithoView skipping processing visibility. But since the parent view was never marked as transient itself, it never had `setHasTransientState(false)` called as well, and we didn't process visibility until the next  `afterMount` or `onVisibleBoundsChanged` when all children were back to non-transient state.

View has a dedicated `childHasTransientStateChanged` to be notified about its children transient state changes, which is being hooked up in this diff to trigger visibility processing when parent's effective transient state is back to `false`.

Reviewed By: adityasharat

Differential Revision: D47841143

fbshipit-source-id: 9a65469ac09af23bb2f2586539b074f5cc5cb1eb

litho-core/src/main/java/com/facebook/litho/BaseMountingView.java

@@ -269,6 +269,34 @@ public void setAnimatedHeight(int height) {
     requestLayout();
   }
 
+  @Override
+  public void childHasTransientStateChanged(View child, boolean childHasTransientState) {
+    final boolean oldHasTransientState = hasTransientState();
+    super.childHasTransientStateChanged(child, childHasTransientState);
+    final boolean newHasTransientState = hasTransientState();
+
+    if (oldHasTransientState == newHasTransientState) {
+      return;
+    }
+
+    if (mTransientStateCount != 0) {
+      return;
+    }
+
+    if (!hasTree()) {
+      return;
+    }
+
+    if (newHasTransientState) {
+      notifyVisibleBoundsChanged(new Rect(0, 0, getWidth(), getHeight()), false);
+    } else {
+      // We mounted everything when the transient state was set on this view. We need to do this
+      // partly to unmount content that is not visible but mostly to get the correct visibility
+      // events to be fired.
+      notifyVisibleBoundsChanged();
+    }
+  }
+
   @Override
   public void setHasTransientState(boolean hasTransientState) {
     super.setHasTransientState(hasTransientState);