DrawingBuffer::prepareBackBuffer,
DrawingBuffer::requiresCopyFromBackToFrontBuffer, and
DrawingBuffer::clearPlatformLayer.
https://bugs.webkit.org/show_bug.cgi?id=118257

Reviewed by Darin Adler.

* platform/graphics/blackberry/DrawingBufferBlackBerry.cpp:
(WebCore::DrawingBuffer::platformLayer):
* platform/graphics/cairo/DrawingBufferCairo.cpp:
(WebCore::DrawingBuffer::paintCompositedResultsToCanvas):
* platform/graphics/clutter/DrawingBufferClutter.cpp:
(WebCore::DrawingBuffer::paintCompositedResultsToCanvas):
* platform/graphics/gpu/DrawingBuffer.cpp:
(WebCore::DrawingBuffer::clear):
* platform/graphics/gpu/DrawingBuffer.h:
* platform/graphics/gpu/mac/DrawingBufferMac.mm:
(WebCore::DrawingBuffer::frontColorBuffer):
* platform/graphics/gpu/qt/DrawingBufferQt.cpp:
(WebCore::DrawingBuffer::paintCompositedResultsToCanvas):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@152240 268f45cc-cd09-0410-ab3c-d52691b4dbfc