Reduce canonicalization when dragging

third_party/WebKit/Source/core/editing/SelectionEditor.cpp

 /*
  * Copyright (C) 2004, 2008, 2009, 2010 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 352 matching lines @@
 void SelectionEditor::updateCachedVisibleSelectionIfNeeded() const {
   // Note: Since we |FrameCaret::updateApperance()| is called from
   // |FrameView::performPostLayoutTasks()|, we check lifecycle against
   // |AfterPerformLayout| instead of |LayoutClean|.
   DCHECK_GE(document().lifecycle().state(),
             DocumentLifecycle::AfterPerformLayout);
   assertSelectionValid();
   if (!needsUpdateVisibleSelection())
     return;
 
+  m_styleVersion = document().styleVersion();
+  m_cacheIsDirty = false;
   m_cachedVisibleSelectionInDOMTree = createVisibleSelection(m_selection);
+  if (m_cachedVisibleSelectionInDOMTree.isNone()) {
+    m_cachedVisibleSelectionInFlatTree = VisibleSelectionInFlatTree();
+    return;
+  }
   m_cachedVisibleSelectionInFlatTree = createVisibleSelection(
       SelectionInFlatTree::Builder()
           .setBaseAndExtent(toPositionInFlatTree(m_selection.base()),
                             toPositionInFlatTree(m_selection.extent()))
           .setAffinity(m_selection.affinity())
           .setHasTrailingWhitespace(m_selection.hasTrailingWhitespace())
           .setGranularity(m_selection.granularity())
           .setIsDirectional(m_selection.isDirectional())
           .build());
-  m_styleVersion = document().styleVersion();
-  m_cacheIsDirty = false;
 }
 
 void SelectionEditor::cacheRangeOfDocument(Range* range) {
   m_cachedRange = range;
 }
 
 Range* SelectionEditor::documentCachedRange() const {
   return m_cachedRange;
 }
 
 void SelectionEditor::clearDocumentCachedRange() {
   m_cachedRange = nullptr;
 }
 
 DEFINE_TRACE(SelectionEditor) {
   visitor->trace(m_frame);
   visitor->trace(m_selection);
   visitor->trace(m_cachedVisibleSelectionInDOMTree);
   visitor->trace(m_cachedVisibleSelectionInFlatTree);
   visitor->trace(m_cachedRange);
   SynchronousMutationObserver::trace(visitor);
 }
 
 }  // namespace blink