Add entry to mb_config.pyl for Linux layout test try bot with flag --enable-slimming-paint-v2.

tools/mb/mb_config.pyl

Index: tools/mb/mb_config.pyl
diff --git a/tools/mb/mb_config.pyl b/tools/mb/mb_config.pyl
index 906d73c5bf1998a942673a2c06e943f948117dc6..f4dfdf2f530120a1f0324af9230db416f268c4be 100644
--- a/tools/mb/mb_config.pyl
+++ b/tools/mb/mb_config.pyl
@@ -775,8 +775,15 @@
       'linux_chromium_webkit_msan_variable': 'findit',
       'linux_chromium_webkit_variable': 'findit',
       'linux_chromiumos_full_variable': 'findit',
-      'linux_nacl_sdk': 'gn_release_bot',
+
+      # This is 'release_bot' rather than 'release_trybot' because
+      # 'release_trybot' includes 'dcheck_always_on', which might cause
+      # some layout test results to be different than for normal release
+      # builds (and we only store baselines for release builds).
+      'linux_layout_tests_slimming_paint_v2': 'swarming_gn_release_bot',
+
       'linux_nacl_sdk_build': 'gn_release_bot',
+      'linux_nacl_sdk': 'gn_release_bot',
       'linux_optional_gpu_tests_rel':
         'swarming_gpu_fyi_tests_gn_release_trybot',
       'linux_site_isolation': 'gn_release_trybot',