sheriff: disable virtual/web-components-v0-disabled/external/wpt/html/dom/reflection-grouping.html

Disable virtual/web-components-v0-disabled/external/wpt/html/dom/reflection-grouping.html
for linux -- it's flaking on "WebKit Linux Leak"

See https://ci.chromium.org/p/chromium/builders/ci/WebKit%20Linux%20Leak/9703

TBR=masonfreed@chromium.org

No-try: true
Bug: 1043774
Change-Id: I729f72639d69fee4288edc29ea1abd0cb73e3fbb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2011283Reviewed-by: Nina Satragno <nsatragno@chromium.org>
Commit-Queue: Nina Satragno <nsatragno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733454}

third_party/blink/web_tests/TestExpectations

@@ -6309,3 +6309,4 @@ crbug.com/1042688 http/tests/devtools/elements/highlight/highlight-dom-updates.j
 
 # Sheriff 2020-01-20
 crbug.com/1043357 http/tests/credentialmanager/credentialscontainer-get-with-virtual-authenticator.html [ Pass Timeout Failure ]
+crbug.com/1043774 [ Linux ] virtual/web-components-v0-disabled/external/wpt/html/dom/reflection-grouping.html [ Pass Failure ]