Re-enable fixed-img-src-change-after-scroll.html

The test seems to not be flaky any more with improvements made to the
web test harness for site isolation. If wrong.. we can revert and
investigate.

Local run of 20 runs had 0 failures and TestExpectations claims it was
very flaky.

R=vmpstr@chromium.org

Bug: 891427
Change-Id: Ic36c6685c5f87f8d1a678a9f88b021f641f18d50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2232767
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775826}

third_party/blink/web_tests/TestExpectations

@@ -1377,8 +1377,6 @@ crbug.com/891427 animations/responsive/viewport-unit-translate-responsive.html [
 crbug.com/891427 virtual/threaded/external/wpt/css/css-scroll-snap/snap-at-user-scroll-end-manual.html [ Pass Failure Timeout Crash ]
 # Next 1 here: https://ci.chromium.org/p/chromium/builders/luci.chromium.try/win7-blink-rel/1504
 crbug.com/891427 tables/mozilla_expected_failures/marvin/table_overflow_dirty_reflow_tbody.html [ Pass Failure Timeout Crash ]
-
-crbug.com/891427 paint/invalidation/scroll/fixed-img-src-change-after-scroll.html [ Pass Failure Timeout Crash ]
 # ====== OOPIF-mode failures until here ======
 
 # ====== Form Controls Refresh (chrome://flags/#form-controls-refresh) failures from here ======

third_party/blink/web_tests/flag-specific/composite-after-paint/paint/invalidation/scroll/fixed-img-src-change-after-scroll-expected.txt

+{
+  "layers": [
+    {
+      "name": "Scrolling background of LayoutView #document",
+      "bounds": [785, 2016],
+      "contentsOpaque": true,
+      "backgroundColor": "#FFFFFF",
+      "transform": 1
+    },
+    {
+      "name": "VerticalScrollbar",
+      "position": [785, 0],
+      "bounds": [15, 600]
+    },
+    {
+      "name": "LayoutImage (positioned) IMG id='img'",
+      "bounds": [100, 100],
+      "transform": 2
+    }
+  ],
+  "transforms": [
+    {
+      "id": 1,
+      "transform": [
+        [1, 0, 0, 0],
+        [0, 1, 0, 0],
+        [0, 0, 1, 0],
+        [0, -1000, 0, 1]
+      ]
+    },
+    {
+      "id": 2,
+      "transform": [
+        [1, 0, 0, 0],
+        [0, 1, 0, 0],
+        [0, 0, 1, 0],
+        [0, 50, 0, 1]
+      ]
+    }
+  ]
+}
+