Reduce canonicalization when dragging

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

Index: third_party/WebKit/Source/core/editing/SelectionEditor.cpp
diff --git a/third_party/WebKit/Source/core/editing/SelectionEditor.cpp b/third_party/WebKit/Source/core/editing/SelectionEditor.cpp
index 14f7509c4de98e7fd4807ce221e35998cc3d7757..5624733f5cd04e17b5801f9c40ccfbc052d27265 100644
--- a/third_party/WebKit/Source/core/editing/SelectionEditor.cpp
+++ b/third_party/WebKit/Source/core/editing/SelectionEditor.cpp
@@ -371,15 +371,19 @@ void SelectionEditor::updateCachedVisibleSelectionIfNeeded() const {
     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;
 }