scroll-snap: Update our existing test to run on threaded mode

At the moment they are mostly flaky but we should/will address them over
time. Enabling these will help us collect data on where the failure are
and allows us to add new tests.

Bug: 878878
Change-Id: I5ede5e9562fc096afbfa5474822f713351ce4ff4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1924907
Commit-Queue: Majid Valipour <majidvp@chromium.org>
Reviewed-by: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721108}

third_party/blink/web_tests/TestExpectations

@@ -6016,3 +6016,12 @@ crbug.com/1029031 http/tests/devtools/user-agent-setting-major-version.js [ Pass
 crbug.com/1029489 http/tests/devtools/elements/elements-linkify-attributes.js [ Pass Failure ]
 crbug.com/1029521 virtual/threaded/external/wpt/web-animations/timing-model/animations/updating-the-finished-state.html [ Pass Failure Timeout ]
 crbug.com/1029541 virtual/threaded/external/wpt/web-animations/timing-model/animations/reverse-running-animation.html [ Pass Failure ]
+
+# Enable scroll-snap tests on impl thread
+# These are currently failing on Mac which needs more investigation, snap-scrolls-visual-viewport seems flaky
+crbug.com/878878 [ Mac ] virtual/threaded/fast/scroll-snap/snaps-after-keyboard-scrolling.html [ Timeout ]
+crbug.com/878878 [ Mac ] virtual/threaded/fast/scroll-snap/snaps-after-scrollbar-scrolling.html [ Timeout ]
+crbug.com/878878 [ Mac ] virtual/threaded/fast/scroll-snap/snaps-for-different-key-granularity.html [ Timeout ]
+
+crbug.com/878878 virtual/threaded/fast/scroll-snap/animate-fling-to-snap-points.html [ Failure Pass Timeout ]
+crbug.com/878878 virtual/threaded/fast/scroll-snap/snap-scrolls-visual-viewport.html [ Failure Pass ]

third_party/blink/web_tests/VirtualTestSuites

@@ -31,6 +31,7 @@
               "external/wpt/requestidlecallback",
               "external/wpt/web-animations/timing-model/animations",
               "fast/events/pointerevents/pinch",
+              "fast/scroll-snap",
               "lifecycle",
               "http/tests/devtools/tracing",
               "http/tests/worklet",

third_party/blink/web_tests/virtual/threaded/fast/scroll-snap/README.txt

+# This suite runs the tests in virtual/threaded/fast/scroll-snap with
+# --enable-threaded-compositing to test scroll snapping on threaded compositing
+# path.
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