Validate all incoming WebGLObjects.

A few entry points were missing the correct validation.

Tested with improved conformance tests in
https://github.com/KhronosGroup/WebGL/pull/2654 .

Bug: 848914
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Ib98a61cc5bf378d1b3338b04acd7e1bc4c2fe008
Reviewed-on: https://chromium-review.googlesource.com/1086718
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565016}
void WebGL2RenderingContextBase::DestroyContext() {
  WebGLRenderingContextBase::DestroyContext();
}

void WebGL2RenderingContextBase::DestroyContext() {
  WebGLRenderingContextBase::DestroyContext();
}
