Compute style-determined compositing reasons during recalc style

LayoutTests/compositing/will-change/gpu-rasterization-hint.html

Index: LayoutTests/compositing/will-change/gpu-rasterization-hint.html
diff --git a/LayoutTests/compositing/will-change/gpu-rasterization-hint.html b/LayoutTests/compositing/will-change/gpu-rasterization-hint.html
index 8fb777c9b2020c0bcbae98a654549fcf0a84a65d..6f3ca8e328f0b5075822282b678b6da98cfd5dfb 100644
--- a/LayoutTests/compositing/will-change/gpu-rasterization-hint.html
+++ b/LayoutTests/compositing/will-change/gpu-rasterization-hint.html
@@ -79,8 +79,11 @@
   </style>
 
   <script>
-    if (window.internals)
+    if (window.internals) {
       window.internals.settings.setAcceleratedCompositingForGpuRasterizationHintEnabled(true);
+      // Force an update of the compositing triggers.
+      window.internals.layerTreeAsText(document);
+    }
 
     if (window.testRunner) {
       testRunner.dumpAsText();