Some speculation about making opaque root finding cheaper.

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

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 23 matching lines @@
 #include "bindings/core/v8/RetainedDOMInfo.h"
 #include "bindings/core/v8/ScriptWrappableVisitor.h"
 #include "bindings/core/v8/V8AbstractEventListener.h"
 #include "bindings/core/v8/V8Binding.h"
 #include "bindings/core/v8/V8Node.h"
 #include "bindings/core/v8/V8ScriptRunner.h"
 #include "bindings/core/v8/WrapperTypeInfo.h"
 #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"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/tracing/TraceEvent.h"
 #include "public/platform/BlameContext.h"
 #include "public/platform/Platform.h"
 #include "wtf/Vector.h"
 #include "wtf/allocator/Partitions.h"
 #include <algorithm>
@@ skipping 31 matching lines @@
     return &document;
   }
 
   if (node->isAttributeNode()) {
     Node* ownerElement = toAttr(node)->ownerElement();
     if (!ownerElement)
       return 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;
 
   return node;
 }
 
 class MinorGCUnmodifiedWrapperVisitor : public v8::PersistentHandleVisitor {
  public:
   explicit MinorGCUnmodifiedWrapperVisitor(v8::Isolate* isolate)
       : m_isolate(isolate) {}
@@ skipping 438 matching lines @@
   double startTime = WTF::currentTimeMS();
   v8::HandleScope scope(isolate);
   PendingActivityVisitor visitor(isolate, executionContext);
   toIsolate(executionContext)->VisitHandlesWithClassIds(&visitor);
   scanPendingActivityHistogram.count(
       static_cast<int>(WTF::currentTimeMS() - startTime));
   return visitor.pendingActivityFound();
 }
 
 }  // namespace blink