Annotate listbox-in-multi-column.html as flaky.

Bug: 798116
Change-Id: I3e13b4f313edac0a951d417b919df0be4332778a
TBR: 
Reviewed-on: https://chromium-review.googlesource.com/847478Reviewed-by: Max Morin <maxmorin@chromium.org>
Commit-Queue: Max Morin <maxmorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526480}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3021,6 +3021,8 @@ crbug.com/734762 inspector-protocol/timeline/page-frames.js [ Failure ]
 crbug.com/736255 [ Mac ] external/wpt/css/vendor-imports/mozilla/mozilla-central-reftests/flexbox/flexbox-baseline-multi-item-vert-001b.html [ Skip ]
 crbug.com/736732 virtual/enable_wasm/external/wpt/wasm/wasm_local_iframe_test.html [ Timeout Pass ]
 
+crbug.com/798116 [ Linux ] fast/forms/select/listbox-in-multi-column.html [ Failure Pass ]
+
 # These imported tests exercise tens of thousands of code points and generate large results. Marked slow, but still timeout.
 crbug.com/736056 [ Mac ] external/wpt/encoding/legacy-mb-japanese [ Timeout Pass ]
 crbug.com/736056 [ Mac Win7 ] external/wpt/encoding/legacy-mb-korean [ Timeout Pass ]