Make SelectionEditor::markCacheDirty() not to reset cached value if it has been cleared

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 e34bba5da6c36786ce4d1ba3d03e039e62164cfa..3cbe4ecee2d19bcee6490b58cb16a34655a86a29 100644
--- a/third_party/WebKit/Source/core/editing/SelectionEditor.cpp
+++ b/third_party/WebKit/Source/core/editing/SelectionEditor.cpp
@@ -123,6 +123,8 @@ bool SelectionEditor::isContentRichlyEditable() const {
 }
 
 void SelectionEditor::markCacheDirty() {
+  if (m_cacheIsDirty)
+    return;
   m_cachedVisibleSelectionInFlatTree = VisibleSelectionInFlatTree();
   m_cachedVisibleSelectionInDOMTree = VisibleSelection();
   m_cacheIsDirty = true;