Re-add expectation for one WPT test on Win7

Removed in https://chromium-review.googlesource.com/c/572261/, however it appears it's still timing out on Win7.

TBR=jeffcarp@chromium.org

Bug: 626703
Change-Id: I06abc7a36886cc4af60065e64d35f8a7be03a1e4
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/575731Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Commit-Queue: Alice Boxhall <aboxhall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487375}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3098,3 +3098,5 @@ crbug.com/717643 external/wpt/html/semantics/scripting-1/the-script-element/modu
 # Sheriff failures 2017-07-03
 crbug.com/708994 http/tests/security/cross-frame-mouse-source-capabilities.html [ Timeout Pass ]
 crbug.com/708994 virtual/mojo-loading/http/tests/security/cross-frame-mouse-source-capabilities.html [ Timeout Pass ]
+
+crbug.com/626703 [ Win7 ] external/wpt/html/semantics/tabular-data/processing-model-1/span-limits.html [ Timeout ]