Add flaky Mac expectation for image-decode-in-frame.html

The test very occasionally times out on Mac 13 and Mac 14.

TBR: vmpstr@chromium.org
Bug: 1054894
Change-Id: Iff9857cd24b84bc2d5c076ac5bef44d86815b608
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2080198Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745573}

third_party/blink/web_tests/TestExpectations

@@ -447,6 +447,9 @@ crbug.com/1056492 external/wpt/svg/painting/reftests/marker-path-001.svg [ Failu
 # Slightly flaky timeouts (about 1 in 30)
 crbug.com/1050993 [ Linux ] virtual/gpu-rasterization/images/drag-image-descendant-painting-sibling.html [ Crash Pass Timeout ]
 
+# Slightly flaky timeouts
+crbug.com/1054894 [ Mac ] http/tests/images/image-decode-in-frame.html [ Pass Timeout ]
+
 # ====== Paint team owned tests to here ======
 
 crbug.com/922249 virtual/android/fullscreen/compositor-touch-hit-rects-fullscreen-video-controls.html [ Failure Pass ]