setSelection should not synchronously trigger layout

setSelection should not synchronously trigger layout
https://bugs.webkit.org/show_bug.cgi?id=128797

Reviewed by Antti Koivisto.

Only update the appearance and reveal selection when the style and the layout is already up to date.
Otherwise, do so in performPostLayoutTasks.

* editing/FrameSelection.cpp:
(WebCore::FrameSelection::FrameSelection):
(WebCore::FrameSelection::setSelection): Set m_pendingSelectionUpdate and synchronously update caret rect
if we don't need to update style or layout.
(WebCore::updateSelectionByUpdatingLayoutOrStyle): Added. Used by FrameSelection member functions to
trigger layout or style recalc whichever is needed.
(WebCore::FrameSelection::updateAndRevealSelection): Extracted from setSelection.
(WebCore::FrameSelection::absoluteCaretBounds): Call updateSelectionByUpdatingLayoutOrStyle since caret rect
is no longer updated synchronously in setSelection.
(WebCore::FrameSelection::recomputeCaretRect): Don't assert that visibleStart().absoluteCaretBounds() is
equal to m_absCaretBounds since selection may no longer be caret at this point.
(WebCore::FrameSelection::setCaretVisibility): Call updateSelectionByUpdatingLayoutOrStyle since we're
synchronously calling into updateAppearance here. In the future, we should make this asynchronous as well.
(WebCore::FrameSelection::selectionBounds): Call updateSelectionByUpdatingLayoutOrStyle since selection bounds
could be outdated. This code only triggering style recalc was presumably a bug.
* editing/FrameSelection.h:

* page/FrameView.cpp:
(WebCore::FrameView::performPostLayoutTasks): Update selection's appearance and scroll to reveal selection
as needed.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@164133 268f45cc-cd09-0410-ab3c-d52691b4dbfc