Separate the geometry update from rebuilding the GraphicsLayer tree

Source/platform/graphics/CompositingReasons.h

Index: Source/platform/graphics/CompositingReasons.h
diff --git a/Source/platform/graphics/CompositingReasons.h b/Source/platform/graphics/CompositingReasons.h
index 513be298323dcc2168b0fc5615a7205fd3245c7a..fc3c8dd22a626c802f3111ab3b76d0cc6d44e529 100644
--- a/Source/platform/graphics/CompositingReasons.h
+++ b/Source/platform/graphics/CompositingReasons.h
@@ -117,6 +117,18 @@ const uint64_t CompositingReasonComboSquashableReasons =
 
 typedef uint64_t CompositingReasons;
 
+// Any reasons other than overlap or assumed overlap will require the layer to be separately compositing.
+inline bool requiresCompositing(CompositingReasons reasons)
+{
+    return reasons & ~CompositingReasonComboSquashableReasons;
+}
+
+// If the layer has overlap or assumed overlap, but no other reasons, then it should be squashed.
+inline bool requiresSquashing(CompositingReasons reasons)
+{
+    return !requiresCompositing(reasons) && (reasons & CompositingReasonComboSquashableReasons);
+}
+
 struct CompositingReasonStringMap {
     CompositingReasons reason;
     const char* shortName;