WebGLRenderingContext.cpp doesn't need to include LayoutBox.h

BUG=614015
TBR=bajones@chromium.org,eae@chromium.org
CQ_INCLUDE_TRYBOTS=tryserver.chromium.win:win_optional_gpu_tests_rel;tryserver.chromium.mac:mac_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2010623002
Cr-Commit-Position: refs/heads/master@{#395846}
1 file changed