Mark shapedetection-cross-origin.html as Timeout on Mac10.11

TBR=mmentovai@chromium.org,carlosk@chromium.org,hendrich@chromium.org

Bug: 732103
No-Try: True
Change-Id: I76813657fdd1b2351901edae03536fe5cddaef59
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1531896Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642427}

third_party/blink/web_tests/TestExpectations

@@ -6138,3 +6138,6 @@ crbug.com/938592 virtual/gpu/fast/canvas/fillrect_gradient.html [ Pass Failure T
 #
 # Trooper 2019-03-19
 crbug.com/836242 [ Mac ] external/wpt/shadow-dom/untriaged/html-elements-in-shadow-trees/html-forms/test-003.html [ Pass Failure ]
+
+# Sheriff 2019-03-20
+crbug.com/732103 [ Mac10.11 ] http/tests/shapedetection/shapedetection-cross-origin.html [ Timeout Pass ]