Calculate the cover rect of tiled backing store with the trajectory vector.

Calculate the cover rect of tiled backing store with the trajectory vector.
https://bugs.webkit.org/show_bug.cgi?id=83462

Patch by JungJik Lee <jungjik.lee@samsung.com> on 2012-04-12
Reviewed by Kenneth Rohde Christiansen.

When trajectory vector is not zero, it is able to calculate the proper cover area.
No new tests - no new functionality.

* platform/graphics/TiledBackingStore.cpp:
(WebCore::TiledBackingStore::computeCoverAndKeepRect):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@113967 268f45cc-cd09-0410-ab3c-d52691b4dbfc