[GTK][WK2] WebGL is not working with GLES
https://bugs.webkit.org/show_bug.cgi?id=126138

Reviewed by Martin Robinson.

m_texture has been unnecessarily regenerated. It's generated in GraphicsContext3D
constructor for offscreen rendering. And m_compositorTexture is used by only Mac port.
They create it in their GraphicsContext3D constructor so that we don't need to recreate it
in GC3DOpenGLES::reshapeFBOs.

No new tests since no functionality changed.

* platform/graphics/cairo/GraphicsContext3DCairo.cpp:
(WebCore::GraphicsContext3D::~GraphicsContext3D):
* platform/graphics/opengl/GraphicsContext3DOpenGL.cpp:
(WebCore::GraphicsContext3D::reshapeFBOs):
* platform/graphics/opengl/GraphicsContext3DOpenGLES.cpp:
(WebCore::GraphicsContext3D::reshapeFBOs):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@160991 268f45cc-cd09-0410-ab3c-d52691b4dbfc