Share FBO state with object and Impl. This patch introduces a new Framebuffer::Data class, which stores attachment related state. This will eliminate the need to store duplicated state between the classes. BUG=angleproject:930 Change-Id: I80de4db39ab99d623b0ad8306bf3cbb794cd8bd5 Reviewed-on: https://chromium-review.googlesource.com/254100 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>