Ensure that detached GraphicsLayers trigger invalidation

GraphicsLayers in this state will not have GraphicsLayer::Paint called on them,
and Paint updates the GraphicsLayer's display item's references back to the
layout tree.

Bug: 991747
Change-Id: I468c0b691fdc8c85414e56dcc6c8a733e666ccc3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1802823
Commit-Queue: Klaus Weidner <klausw@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696449}

third_party/blink/renderer/platform/graphics/graphics_layer.cc

@@ -209,6 +209,13 @@ void GraphicsLayer::RemoveFromParent() {
     SetParent(nullptr);
   }
 
+  // Avoid inconsistencies for detached content since GraphicsLayers in that
+  // state will not have GraphicsLayer::Paint called on them, and Paint updates
+  // the GraphicsLayer's display item's references back to the layout tree.
+  // Only do this if there's a paint controller.
+  if (PaintsContentOrHitTest())
+    GetPaintController().InvalidateAll();
+
   // cc::Layers are created and removed in PaintArtifactCompositor so ensure it
   // is notified that something has changed.
   client_.GraphicsLayersDidChange();