Mark shift-relative-positioned-container-with-image-addition as flaky

Can't preemptively mark Mac as flaky, because it needs a rebaseline.  :(

TBR=jchaffraix@chromium.org
BUG=356834

Review URL: https://codereview.chromium.org/212623005

git-svn-id: svn://svn.chromium.org/blink/trunk@170099 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/LayoutTests/TestExpectations

@@ -802,6 +802,8 @@ crbug.com/337735 [ Linux ] virtual/softwarecompositing/overflow/iframe-scroll-ch
 
 crbug.com/349552 [ Android ] compositing/animation/animated-composited-inside-hidden.html [ Pass Timeout ]
 
+crbug.com/356834 [ Linux Android Win ] fast/repaint/shift-relative-positioned-container-with-image-addition.html [ Pass Failure ]
+
 crbug.com/333882 [ Win ] inspector/editor/text-editor-selection-to-search.html [ Pass Failure ]
 crbug.com/333882 [ Win ] inspector/elements/edit-trimmed-attribute-value.html [ Pass Failure ]
 crbug.com/333882 [ Win7 ] inspector/elements/styles/styles-change-node-while-editing.html [ Pass Failure ]