Fix bug link for failing tests in external/wpt/css/css-position-3/

BUG=728527
NOTRY=true
TBR=smcgruer@chromium.org

Change-Id: Ia880080ed5b84dc6cebe5bf73e84fc100ad5074a
Reviewed-on: https://chromium-review.googlesource.com/520386Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Commit-Queue: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#476269}

third_party/WebKit/LayoutTests/TestExpectations

@@ -127,8 +127,8 @@ crbug.com/719533 compositing/overflow/absolute-element-in-isolated-composited-an
 #### external/wpt/css/css-position-3
 crbug.com/702927 external/wpt/css/css-position-3/position-sticky-table-tr-top.html [ Failure ]
 crbug.com/702927 external/wpt/css/css-position-3/position-sticky-table-tr-bottom.html [ Failure ]
-crbug.com/728527 external/wpt/css/css-position-3/position-sticky-table-tfoot-bottom.html [ Failure ]
-crbug.com/728527 external/wpt/css/css-position-3/position-sticky-table-thead-top.html [ Failure ]
+crbug.com/702927 external/wpt/css/css-position-3/position-sticky-table-tfoot-bottom.html [ Failure ]
+crbug.com/702927 external/wpt/css/css-position-3/position-sticky-table-thead-top.html [ Failure ]
 
 # ====== Layout team owned tests from here ======