Run layout tests w/ --debug on linux-blink-heap-incremental-marking.

Bug: 812533
Change-Id: I4a4d804bdeee453096b191716273e0aaf0ff5de8
Reviewed-on: https://chromium-review.googlesource.com/943597
Reviewed-by: Dirk Pranke <[email protected]>
Commit-Queue: John Budorick <[email protected]>
Cr-Commit-Position: refs/heads/master@{#540574}
diff --git a/testing/buildbot/test_suite_exceptions.pyl b/testing/buildbot/test_suite_exceptions.pyl
index 85f70d8..d0a4467 100644
--- a/testing/buildbot/test_suite_exceptions.pyl
+++ b/testing/buildbot/test_suite_exceptions.pyl
@@ -3637,6 +3637,11 @@
           'shards': 6,
         },
       },
+      'linux-blink-heap-incremental-marking': {
+        'args': [
+          '--debug',
+        ],
+      },
       'WebKit Linux layout_ng Dummy Builder': {
         'args': [
           '--additional-driver-flag=--enable-blink-features=LayoutNG',