Fix inconsistent text selection behavior with option-shift-left/right/up/down.

Fix inconsistent text selection behavior with option-shift-left/right/up/down.
https://bugs.webkit.org/show_bug.cgi?id=75652

Patch by Pablo Flouret <pablof@motorola.com> on 2012-01-19
Reviewed by Enrica Casucci.

On Mac, selecting backwards by word, line or paragraph from the middle
of some text, and then going forward leaves the caret back in the middle
with no selection, instead of directly selecting to the other end of the
word/line/paragraph (Unix/Windows behavior). Fix this by adding a new
editing behavior to control whether the selection should go across the
initial position of the caret directly or not in situations like the one
outlined above.

Source/WebCore:

Test: editing/selection/selection-extend-should-not-move-across-caret-on-mac.html

* editing/EditingBehavior.h:
(WebCore::EditingBehavior::shouldExtendSelectionByWordOrLineAcrossCaret):
* editing/FrameSelection.cpp:
(WebCore::FrameSelection::modify):

LayoutTests:

* editing/selection/selection-extend-should-not-move-across-caret-on-mac-expected.txt: Added.
* editing/selection/selection-extend-should-not-move-across-caret-on-mac.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105473 268f45cc-cd09-0410-ab3c-d52691b4dbfc