Re-enable WPT flexbox-baseline-multi-item-vert-001b

It seems that external/wpt/css/vendor-imports/mozilla/...
   mozilla-central-reftests/flexbox/...
   flexbox-baseline-multi-item-vert-001b.html
has been passing consistently for as long as the flakiness
dashboard has history now.

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#
   testType=webkit_layout_tests&
   tests=flexbox-baseline-multi-item-vert-001b.html

This test also seems to pass on the Mac bots, so we might
just as well enable it there at the same time.

Bug: 736255,626703
Change-Id: I008407bfd4cf65c88d60b2095ecb58c4dd5a2cce
Reviewed-on: https://chromium-review.googlesource.com/1133304Reviewed-by: Robert Flack <flackr@chromium.org>
Commit-Queue: Peter Mayo <petermayo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575267}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3440,7 +3440,6 @@ crbug.com/626703 external/wpt/xhr/setrequestheader-header-allowed.htm [ Failure
 crbug.com/626703 [ Linux Win ] external/wpt/css/selectors/selector-placeholder-shown-type-change-001.html [ Failure ]
 crbug.com/626703 [ Linux Win ] external/wpt/css/selectors/selector-read-write-type-change-002.html [ Failure ]
 crbug.com/626703 [ Linux Win ] external/wpt/css/selectors/selector-required-type-change-002.html [ Failure ]
-crbug.com/626703 [ Linux Win ] external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox/flexbox-baseline-multi-item-vert-001b.html [ Failure ]
 crbug.com/626703 [ Mac ] external/wpt/2dcontext/the-canvas-state/canvas_state_restore_001.htm [ Failure ]
 crbug.com/626703 [ Mac ] external/wpt/css/css-flexbox/auto-margins-001.html [ Failure ]
 crbug.com/626703 [ Win10 ] external/wpt/preload/delaying-onload-link-preload-after-discovery.html [ Timeout ]
@@ -3862,8 +3861,6 @@ crbug.com/737959 http/tests/misc/video-poster-image-load-outlives-gc-without-cra
 
 crbug.com/734762 inspector-protocol/timeline/page-frames.js [ Failure Pass ]
 
-crbug.com/736255 [ Mac ] external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox/flexbox-baseline-multi-item-vert-001b.html [ Skip ]
-
 # module script lacks XHTML support
 crbug.com/717643 external/wpt/html/semantics/scripting-1/the-script-element/module/module-in-xhtml.xhtml [ Failure ]