Gardening: clean a few expectations

marked as mac only
virtual/gpu/compositedscrolling/scrollbars/custom-scrollbar-with-incomplete-style.html [ ImageOnlyFailure ]

removed:
svg/as-object/nested-embedded-svg-size-changes.html [ Crash ]
editing/context-menu-leak-document.html [ Failure ]

marked as Debug only
svg/as-object/deep-nested-embedded-svg-size-changes-no-layout-triggers-1.html [ Crash ]
svg/as-object/deep-nested-embedded-svg-size-changes-no-layout-triggers-2.html [ Crash ]

BUG=
TBR=ojan
NOTRY=true

Review URL: https://codereview.chromium.org/270633011

git-svn-id: svn://svn.chromium.org/blink/trunk@173631 bbb929c8-8fbe-4397-9dbb-9b2b20218538