Make IOSurface::Locker and use it in ImageBufferDataCG

Make IOSurface::Locker and use it in ImageBufferDataCG
https://bugs.webkit.org/show_bug.cgi?id=180317

Reviewed by Zalan Bujtas.

Add an RAII IOSurface::Locker which can lock readonly or readwrite. Access
to the IOSurface base address is through the locker.

Add IOSurface::bytesPerRow() to wrap IOSurfaceGetBytesPerRow().

After this, there is only one location where we access the IOSurfaceRef
directly, in WebGL code.

* platform/graphics/cg/ImageBufferDataCG.cpp:
(WebCore::ImageBufferData::toBGRAData const):
(WebCore::ImageBufferData::getData const):
(WebCore::ImageBufferData::putData):
* platform/graphics/cocoa/IOSurface.h:
* platform/graphics/cocoa/IOSurface.mm:
(WebCore::IOSurface::bytesPerRow const):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@225454 268f45cc-cd09-0410-ab3c-d52691b4dbfc