Don't build gl_lpm_fuzzer on ChromeOS

Building this binary works fine but initializing GL fails when we
run it. Since we are already fuzzing this successfully on Linux
there's no need to replicate that effort on ChromeOS.

Bug: 967220
Change-Id: Ie59988d860614d9d23e213ea52c52224660eac06
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1636855Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Ned Williamson <nedwill@google.com>
Cr-Commit-Position: refs/heads/master@{#665316}

gpu/BUILD.gn

@@ -197,7 +197,7 @@ jumbo_static_library("test_support") {
   ]
 }
 
-if (!is_android && !is_fuchsia) {
+if (!is_android && !is_fuchsia && !is_chromeos) {
   proto_library("gl_lpm_fuzzer_proto") {
     sources = [
       "command_buffer/tests/lpm/gl_lpm_fuzzer.proto",