WebCore: Can focus but not type into content editable block that contains only non-editable content.
<rdar://problem/5982901>
https://bugs.webkit.org/show_bug.cgi?id=31750
        
Reviewed by Darin Adler.

The goal is to change the way we choose a visible position
after hit detection, by preferring a visually equivalent editable
position if available. By doing this, it is possible to add content
to an editable block that initially contains only non editable elements.

Test: editing/selection/mixed-editability-10.html

* WebCore.base.exp: Changed to match the new signature of downstream
and upstream in the Position class.
* dom/Position.cpp:
(WebCore::Position::atEditingBoundary): Added.
(WebCore::Position::upstream): Modified to allow to cross the boundary
between editable and non editable content if required.
(WebCore::Position::downstream): Modified to allow to cross the boundary
between editable and non editable content if required.
(WebCore::Position::isCandidate): Modified to qualify as candidates positions
that are at the editability boundary.
(WebCore::Position::getInlineBoxAndOffset): Modified to retrieve the inline box
to be used in calculating the caret rectangle.
* dom/Position.h:
(WebCore::Position::):
* dom/PositionIterator.cpp:
(WebCore::PositionIterator::atEditingBoundary): Added.
(WebCore::PositionIterator::isCandidate): Modified to qualify as candidates positions
that are at the editability boundary.
* dom/PositionIterator.h:
* editing/htmlediting.cpp:
(WebCore::firstEditablePositionAfterPositionInRoot): Modified to accept not only
descendants of the editable container, but the container itself.
(WebCore::lastEditablePositionBeforePositionInRoot): Modified to accept not only
descendants of the editable container, but the container itself.
* rendering/RenderObject.cpp:
(WebCore::RenderObject::createVisiblePosition): Added logic to prefer an editable position,
if available.
* rendering/RenderText.cpp:
(WebCore::RenderText::isAllCollapsibleWhitespace): Added.
* rendering/RenderText.h:

LayoutTests: Can focus but not type into content editable block that contains only non-editable content.
<rdar://problem/5982901>
https://bugs.webkit.org/show_bug.cgi?id=31750

Reviewed by Darin Adler.

* editing/selection/5825350-1-expected.txt:
* editing/selection/5825350-1.html: Modified to use caret rectangle.
* editing/selection/5825350-2-expected.txt:
* editing/selection/5825350-2.html: Modified to use caret rectangle.
* editing/selection/mixed-editability-10-expected.txt: Added.
* editing/selection/mixed-editability-10.html: Added.
* platform/mac/editing/deleting/5390681-2-expected.txt: Re-baselined
to account for the new possible caret position.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@51522 268f45cc-cd09-0410-ab3c-d52691b4dbfc