Flag canvas-colorManaged-convertToBlob-roundtrip.html to timeout

fast/canvas/color-space/canvas-colorManaged-convertToBlob-roundtrip.html
virtual/gpu/fast/canvas/color-space/canvas-colorManaged-convertToBlob-roundtrip.html

They flakily time out.

TBR=fserb
NOTRY=true

Bug: 851746
Change-Id: Ib32001de56c74350a016e124fb5fa7e8906b5b04
Reviewed-on: https://chromium-review.googlesource.com/1126202Reviewed-by: Mohammad Reza Zakerinasab <zakerinasab@chromium.org>
Commit-Queue: Mohammad Reza Zakerinasab <zakerinasab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572561}

third_party/WebKit/LayoutTests/TestExpectations

@@ -4670,6 +4670,8 @@ crbug.com/851090 virtual/mouseevent_fractional/fast/events/middleClickAutoscroll
 
 # Sheriff 2018-06-11
 crbug.com/850202 [ Linux ] http/tests/devtools/network/network-filters.js [ Pass Failure ]
+crbug.com/851746 [ Linux ] fast/canvas/color-space/canvas-colorManaged-convertToBlob-roundtrip.html [ Pass Timeout ]
+crbug.com/851746 [ Linux ] virtual/gpu/fast/canvas/color-space/canvas-colorManaged-convertToBlob-roundtrip.html [ Pass Timeout ]
 
 crbug.com/853360 [ Mac ] fast/css/input-search-padding.html [ Failure ]
 crbug.com/853360 [ Mac ] fast/forms/calendar-picker/calendar-picker-appearance-ar.html [ Failure ]