1) make RenderTextureHost into a abstract base class for all RenderXXXTextureHost.
2) create a base class RenderTextureHostOGL for all texture handle base texture.
3) create RenderBufferTextureHost for buffer texture at render thread.
4) create RenderMacIOSurfaceTextureHostOGL for MacIOSurface at render thread.
--HG--
rename : gfx/webrender_bindings/RenderBufferTextureHost.h => gfx/webrender_bindings/RenderTextureHost.h
JerryShih