Validate before calling glDrawBuffers with the passthrough decoder.

BUG=1043460

Change-Id: Iceab4aa65cb50bbe3be706cdfdee1564b8158298
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2081517Reviewed-by: Jonah Ryan-Davis (use @google.com) <jonahr@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746025}

gpu/command_buffer/service/gles2_cmd_decoder_passthrough_doers.cc

@@ -4691,6 +4691,11 @@ error::Error GLES2DecoderPassthroughImpl::DoDescheduleUntilFinishedCHROMIUM() {
 error::Error GLES2DecoderPassthroughImpl::DoDrawBuffersEXT(
     GLsizei count,
     const volatile GLenum* bufs) {
+  if (!feature_info_->feature_flags().ext_draw_buffers &&
+      !feature_info_->gl_version_info().is_es3) {
+    return error::kUnknownCommand;
+  }
+
   // Validate that count is non-negative before allocating a vector
   if (count < 0) {
     InsertError(GL_INVALID_VALUE, "count cannot be negative.");