Mark virtual/gpu/fast/canvas/canvas-blend-image.html as slow on all platforms

TBR=paint-dev@chromium.org

BUG=866850

Change-Id: Ie0d11b263efc504ba7e7e15631c1af098bf4fcba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1750507Reviewed-by: Fergus Dall <sidereal@google.com>
Cr-Commit-Position: refs/heads/master@{#686307}

third_party/blink/web_tests/SlowTests

@@ -287,8 +287,7 @@ crbug.com/910627 webexposed/global-interface-listing-shared-worker.html [ Slow ]
 crbug.com/910627 virtual/stable/webexposed/global-interface-listing-shared-worker.html [ Slow ]
 
 ### virtual/gpu/fast/canvas/ blending layout tests are slow
-crbug.com/866850 [ Linux ] virtual/gpu/fast/canvas/canvas-blend-image.html [ Slow ]
-crbug.com/866850 [ Mac ] virtual/gpu/fast/canvas/canvas-blend-image.html [ Slow ]
+crbug.com/866850 virtual/gpu/fast/canvas/canvas-blend-image.html [ Slow ]
 crbug.com/866850 [ Linux ] virtual/gpu/fast/canvas/canvas-blending-color-over-image.html [ Slow ]
 crbug.com/866850 [ Mac ] virtual/gpu/fast/canvas/canvas-blending-color-over-image.html [ Slow ]
 crbug.com/866850 [ Linux ] virtual/gpu/fast/canvas/canvas-blending-color-over-pattern.html [ Slow ]