Do not send redundant selectionchange-events (decouple focus)

third_party/WebKit/Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc.
  * All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
@@ skipping 2663 matching lines @@
     // animations) is difficult, for now we match IE's heuristic and bring
     // up the keyboard if there's been any gesture since load.
     document().page()->chromeClient().showVirtualKeyboardOnElementFocus();
   }
 }
 
 void Element::updateFocusAppearance(
     SelectionBehaviorOnFocus selectionBehavior) {
   if (selectionBehavior == SelectionBehaviorOnFocus::None)
     return;
+
+  LocalFrame* frame = document().frame();

[yosin_UTC9, 2017/02/09 13:02:17]

We can early return here if |!frame|.
Let's hoist |if (!frame)| at L2687 here.

   if (isRootEditableElement(*this)) {
-    LocalFrame* frame = document().frame();
     if (!frame)
       return;
 
     // When focusing an editable element in an iframe, don't reset the selection
     // if it already contains a selection.
     if (this == frame->selection().rootEditableElement())
       return;
 
     // TODO(xiaochengh): The use of updateStyleAndLayoutIgnorePendingStylesheets
     // needs to be audited.  See http://crbug.com/590369 for more details.
     document().updateStyleAndLayoutIgnorePendingStylesheets();
 
     // FIXME: We should restore the previous selection if there is one.
     // Passing DoNotSetFocus as this function is called after
     // FocusController::setFocusedElement() and we don't want to change the
     // focus to a new Element.
     frame->selection().setSelection(
         SelectionInDOMTree::Builder()
             .collapse(firstPositionInOrBeforeNode(this))
             .build(),
         FrameSelection::CloseTyping | FrameSelection::ClearTypingStyle |
             FrameSelection::DoNotSetFocus);
     frame->selection().revealSelection();
-  } else if (layoutObject() && !layoutObject()->isLayoutPart()) {
-    layoutObject()->scrollRectToVisible(boundingBox());
+  } else {
+    // This element is non editable.
+    if (frame)
+      frame->selection().clear();

[yosin_UTC9, 2017/02/09 13:02:17]

Focus and selection are individual identity. We don't want to clear focus here.
Think about caret browsing is an example although chrome doesn't support caret
browsing anymore.

[hugoh_UTC2, 2017/02/11 03:42:22]

True, here we would clear() too often. Let's put this logic in
advanceFocusInDocumentOrder() instead? When tabbing from <input> to <button> the
selected text of <input> should be cleared. Otherwise, we change the current
behavior of tab/shift+tab.

+
+    if (layoutObject() && !layoutObject()->isLayoutPart())
+      layoutObject()->scrollRectToVisible(boundingBox());
   }
 }
 
 void Element::blur() {
   cancelFocusAppearanceUpdate();
   if (adjustedFocusedElementInTreeScope() == this) {
     Document& doc = document();
     if (doc.page())
       doc.page()->focusController().setFocusedElement(0, doc.frame());
     else
@@ skipping 1413 matching lines @@
 }
 
 DEFINE_TRACE_WRAPPERS(Element) {
   if (hasRareData()) {
     visitor->traceWrappers(elementRareData());
   }
   ContainerNode::traceWrappers(visitor);
 }
 
 }  // namespace blink