Mark a context_lost test flaky on Mac ASAN.

GpuCrash_GPUProcessCrashesExactlyOncePerVisitToAboutGpuCrash
occasionally crashes the renderer process while navigating to
about:gpucrash. The test's main tab appears to crash too.

Required passing an --is-asan argument to the test, similarly to the
WebGL conformance tests.

Bug: 861956
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: Ic18876e88a0d99c9152be1a67599f2cae3cd4881
Tbr: jmadill@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/1130507
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573577}
diff --git a/testing/buildbot/test_suite_exceptions.pyl b/testing/buildbot/test_suite_exceptions.pyl
index acda218..33d7d97 100644
--- a/testing/buildbot/test_suite_exceptions.pyl
+++ b/testing/buildbot/test_suite_exceptions.pyl
@@ -961,6 +961,15 @@
       },
     },
   },
+  'context_lost_tests': {
+    'modifications': {
+      'Mac FYI GPU ASAN Release': {
+        'args': [
+          '--is-asan',
+        ]
+      },
+    },
+  },
   'crashpad_tests': {
     'remove_from': [
       # chromium.clang