Some speculation about making opaque root finding cheaper.

third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp

Index: third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp b/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
index 87d93525711c43f86222e5707988b4ec1ec0a64f..9b4ebfde87ab90475bf8359d4f54a2b1a24be015 100644
--- a/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/V8GCController.cpp
@@ -41,6 +41,7 @@
 #include "core/dom/Attr.h"
 #include "core/dom/Element.h"
 #include "core/dom/Node.h"
+#include "core/dom/shadow/ShadowRoot.h"
 #include "core/html/imports/HTMLImportsController.h"
 #include "core/inspector/InspectorTraceEvents.h"
 #include "platform/Histogram.h"
@@ -92,6 +93,13 @@ Node* V8GCController::opaqueRootForGC(v8::Isolate*, Node* node) {
     node = ownerElement;
   }
 
+  // Node -> Host (if any) is O(1)
+  while (node->isInShadowTree())
+    node = &node->containingShadowRoot()->host();
+
+  // The "ShadowHost" part is redundant because of the isInShadowTree
+  // loop, but this is still preferable because parent/shadow host
+  // pointer occupies the same space.
   while (Node* parent = node->parentOrShadowHostOrTemplateHostNode())
     node = parent;