Mark offscreencanvas tests as flaky on Linux.

third_party/WebKit/LayoutTests/TestExpectations

Index: third_party/WebKit/LayoutTests/TestExpectations
diff --git a/third_party/WebKit/LayoutTests/TestExpectations b/third_party/WebKit/LayoutTests/TestExpectations
index 277acc5c1c924326255b911bdd75e1f5d39ee49b..77db6357d77bb01853c28bb0ff1ffe2f15ea9b41 100644
--- a/third_party/WebKit/LayoutTests/TestExpectations
+++ b/third_party/WebKit/LayoutTests/TestExpectations
@@ -2230,8 +2230,8 @@ crbug.com/674468 [ Trusty ] compositing/reflections/nested-reflection-transition
 crbug.com/674720 [ Debug Trusty ] http/tests/loading/preload-img-test.html [ Pass Failure ]
 
 # Added 2016-12-16
-crbug.com/674858 [ Trusty ] virtual/threaded/printing/offscreencanvas-2d-printing.html [ Pass Failure ]
-crbug.com/674858 [ Trusty ] virtual/threaded/printing/offscreencanvas-webgl-printing.html [ Pass Failure ]
+crbug.com/674858 [ Linux ] virtual/threaded/printing/offscreencanvas-2d-printing.html [ Pass Failure ]
+crbug.com/674858 [ Linux ] virtual/threaded/printing/offscreencanvas-webgl-printing.html [ Pass Failure ]
 
 # for Skia DEPS roll
 crbug.com/674509   compositing/overlap-blending/reflection-opacity-huge.html [ NeedsRebaseline ]