Get rid of redundant layout tree update related to selection

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights
  * reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  * Copyright (C) 2015 Google 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:
@@ skipping 1033 matching lines @@
 
 bool SelectionController::mouseDownMayStartSelect() const {
   return m_mouseDownMayStartSelect;
 }
 
 bool SelectionController::mouseDownWasSingleClickInSelection() const {
   return m_mouseDownWasSingleClickInSelection;
 }
 
 void SelectionController::notifySelectionChanged() {
-  if (selection().getSelectionType() == SelectionType::RangeSelection)
-    m_selectionState = SelectionState::ExtendedSelection;
-  else if (selection().getSelectionType() == SelectionType::CaretSelection)
-    m_selectionState = SelectionState::PlacedCaret;
-  else
-    m_selectionState = SelectionState::HaveNotStartedSelection;
+  // To avoid regression on speedometer benchmark[1] test, we should not
+  // update layout tree in this code block.
+  // [1] http://browserbench.org/Speedometer/
+  DocumentLifecycle::DisallowTransitionScope disallowTransition(
+      m_frame->document()->lifecycle());
+
+  const SelectionInDOMTree& selection = this->selection().selectionInDOMTree();
+  switch (selection.selectionTypeWithLegacyGranularity()) {
+    case NoSelection:
+      m_selectionState = SelectionState::HaveNotStartedSelection;
+      return;
+    case CaretSelection:
+      m_selectionState = SelectionState::PlacedCaret;
+      return;
+    case RangeSelection:
+      m_selectionState = SelectionState::ExtendedSelection;
+      return;
+  }
+  NOTREACHED() << "We should handle all SelectionType" << selection;
 }
 
 FrameSelection& SelectionController::selection() const {
   return m_frame->selection();
 }
 
 bool isLinkSelection(const MouseEventWithHitTestResults& event) {
   return (event.event().modifiers() & WebInputEvent::Modifiers::AltKey) != 0 &&
          event.isOverLink();
 }
 
 bool isExtendingSelection(const MouseEventWithHitTestResults& event) {
   bool isMouseDownOnLinkOrImage =
       event.isOverLink() || event.hitTestResult().image();
   return (event.event().modifiers() & WebInputEvent::Modifiers::ShiftKey) !=
              0 &&
          !isMouseDownOnLinkOrImage;
 }
 
 }  // namespace blink