Try to do less work clearing the font-cache in StyleEngine::didDetach.

third_party/WebKit/Source/core/dom/StyleEngine.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
@@ skipping 433 matching lines @@
 }
 
 void StyleEngine::didDetach() {
   clearResolvers();
   m_globalRuleSet.dispose();
   m_treeBoundaryCrossingScopes.clear();
   m_dirtyTreeScopes.clear();
   m_activeTreeScopes.clear();
   m_viewportResolver = nullptr;
   m_mediaQueryEvaluator = nullptr;
-  clearFontCache();
+  if (m_fontSelector)
+    m_fontSelector->fontFaceCache()->clearAll();
+  m_fontSelector = nullptr;
 }
 
 void StyleEngine::clearFontCache() {
   if (m_fontSelector)
     m_fontSelector->fontFaceCache()->clearCSSConnected();
   if (m_resolver)
     m_resolver->invalidateMatchedPropertiesCache();
 }
 
 void StyleEngine::updateGenericFontFamilySettings() {
@@ skipping 670 matching lines @@
 }
 
 DEFINE_TRACE_WRAPPERS(StyleEngine) {
   for (auto sheet : m_injectedAuthorStyleSheets) {
     visitor->traceWrappers(sheet);
   }
   visitor->traceWrappers(m_documentStyleSheetCollection);
 }
 
 }  // namespace blink