Merge skia/ImageSourceSkia.cpp into ImageSource.cpp.

Reviewed by Adam Treat.

* WebCore.gypi: Remove deleted file, plus a file that was deleted a while back.
* platform/graphics/ImageSource.cpp:
(WebCore::ImageSource::setData): Use slightly shorter syntax.
(WebCore::ImageSource::filenameExtension): Use shorter syntax.
(WebCore::ImageSource::createFrameAtIndex): Remove redundant call, clarify comments, reject all empty images.
(WebCore::ImageSource::frameHasAlphaAtIndex): Clarify comments, use shorter syntax.
* platform/graphics/skia/ImageSourceSkia.cpp: Removed.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@47081 268f45cc-cd09-0410-ab3c-d52691b4dbfc