Simplify ReplaceSelectionCommand::positionAtStartOfInsertedContent

Simplify ReplaceSelectionCommand::positionAtStartOfInsertedContent
https://bugs.webkit.org/show_bug.cgi?id=68939

Reviewed by Darin Adler.

Simplified ReplaceSelectionCommand::positionAtStartOfInsertedContent.

This change revealed a bug in removeUnrenderedTextNodesAtEnds that text nodes without any visible
text at ends are not removed when it has a render object. Fixed the bug by checking the length of
the rendered text. (Tested by editing/pasteboard/pasting-word-in-div-extra-line.html)

This further revealed that caretMaxRenderedOffset doesn't return an offset and caretMaxRenderedOffset
on InlineBox, InlineTextBox, RenderObject, RenderBR, RenderPlaced are never called. To address this
issue, renamed caretMaxRenderedOffset to renderedTextLength for RenderText and removed the rest.

* dom/Position.cpp:
(WebCore::Position::rendersInDifferentPosition):
* editing/ReplaceSelectionCommand.cpp:
(WebCore::nodeHasVisibleRenderText): Added.
(WebCore::ReplaceSelectionCommand::removeUnrenderedTextNodesAtEnds): Calls nodeHasVisibleRenderText.
(WebCore::ReplaceSelectionCommand::positionAtStartOfInsertedContent): Simplified.
* editing/visible_units.cpp:
(WebCore::startOfParagraph): Calls renderedTextLength.
(WebCore::endOfParagraph): Ditto.
* rendering/InlineBox.cpp: Removed caretMaxRenderedOffset.
* rendering/InlineBox.h: Ditto.
* rendering/InlineTextBox.cpp: Ditto.
* rendering/InlineTextBox.h: Ditto.
* rendering/RenderBR.cpp: Ditto.
* rendering/RenderBR.h: Ditto.
* rendering/RenderObject.cpp: Ditto.
* rendering/RenderObject.h: Ditto.
* rendering/RenderReplaced.cpp: Ditto.
* rendering/RenderReplaced.h: Ditto.
* rendering/RenderText.cpp:
(WebCore::RenderText::renderedTextLength): Renamed from caretMaxRenderedOffset.
* rendering/RenderText.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@96187 268f45cc-cd09-0410-ab3c-d52691b4dbfc