Patch by Robin Qiu <robin.qiu@torchmobile.com.cn> on 2011-07-19

Reviewed by Antonio Gomes.

ScrollBar should initialize current position in constructor.
https://bugs.webkit.org/show_bug.cgi?id=39284

When ScrollBar is created, m_currentPos should be initialized to
m_scrollableArea's current scrollPosition. Because scrollbars may
be created after the content of m_scrollableArea has been scrolled.

Source/WebCore:

Test: scrollbars/scrollbar-initial-position.html

* platform/Scrollbar.cpp:
(WebCore::Scrollbar::Scrollbar):

LayoutTests:

* scrollbars/scrollbar-initial-position-expected.png: Added.
* scrollbars/scrollbar-initial-position-expected.txt: Added.
* scrollbars/scrollbar-initial-position.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@91244 268f45cc-cd09-0410-ab3c-d52691b4dbfc