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 353 matching lines @@
   // 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_cachedVisibleSelectionInDOMTree = createVisibleSelection(m_selection);
-  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());
+  if (m_cachedVisibleSelectionInDOMTree.isNone()) {

[yosin_UTC9, 2017/03/16 02:30:05]

Good catch!

Please move this shortcut in another patch.

We would like to split SelectionEditor::udpateCahceVisibleSelectionIfNeeded()
into to one for DOM tree and another for Flat Tree.
We don't need to compute DOM tree version and Flat Tree version same time, e.g.
execCommand() only needs DOM tree version and painting needs only Flat Tree
version.

This is my mistake that having only one cache.

[yoichio, 2017/03/16 04:10:59]

This is core of this CL and needs for performance improvement.
We should do with fixing dragging selection code 

+    m_cachedVisibleSelectionInFlatTree = VisibleSelectionInFlatTree();
+  } else {
+    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