Code:  GLboolean WebGLRenderingContextBase::isRenderbuffer(
     WebGLRenderbuffer* renderbuffer) {
  if (!renderbuffer || isContextLost())
     return 0;
 
   if (!renderbuffer->HasEverBeenBound())
    return 0;
  if (renderbuffer->IsDeleted())
    return 0;

  return ContextGL()->IsRenderbuffer(renderbuffer->Object());
 }

Vulnerability Type: Overflow 
CWE ID: CWE-119
Summary: Insufficient data validation in WebGL in Google Chrome prior to 68.0.3440.75 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.
Commit Message: 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}