Add virtual test suite for isInputPending WPTs

Enables threaded compositing and cross-origin iframe layerization to allow WPTs to pass.

Bug: 910421
Change-Id: Id79d93eb23c36181c0091a7ee8b4164387ea9308
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2380813Reviewed-by: Stefan Zager <szager@chromium.org>
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Cr-Commit-Position: refs/heads/master@{#803295}

third_party/blink/web_tests/FlagExpectations/composite-after-paint

@@ -60,3 +60,7 @@ crbug.com/1106550 virtual/threaded-prefer-compositing/fast/scrolling/scrollbars/
 # Need to force the video to be composited in this case, or change pre-CAP
 # to match CAP behavior.
 crbug.com/1108972 fullscreen/compositor-touch-hit-rects-fullscreen-video-controls.html [ Failure ]
+
+# Cross-origin iframe layerization is buggy with empty iframes.
+crbug.com/1123189 virtual/threaded-composited-iframes/external/wpt/is-input-pending/security/cross-origin-subframe-masked-pointer-events-mixed-2.sub.html [ Failure ]
+crbug.com/1123189 virtual/threaded-composited-iframes/external/wpt/is-input-pending/security/cross-origin-subframe-complex-clip.sub.html [ Failure ]

third_party/blink/web_tests/TestExpectations

@@ -2202,7 +2202,10 @@ crbug.com/893480 external/wpt/infrastructure/testdriver/actions/multiDevice.html
 crbug.com/893480 external/wpt/pointerevents/pointerevent_touch-action-keyboard.html [ Failure Timeout ]
 crbug.com/893480 external/wpt/infrastructure/testdriver/actions/actionsWithKeyPressed.html [ Failure Timeout ]
 crbug.com/893480 external/wpt/css/css-scroll-snap/input/keyboard.html [ Failure Timeout ]
-crbug.com/893480 external/wpt/is-input-pending/tentative/* [ Failure Timeout ]
+
+# isInputPending requires threaded compositing and layerized iframes
+crbug.com/910421 external/wpt/is-input-pending/* [ Skip ]
+crbug.com/910421 virtual/threaded-composited-iframes/external/wpt/is-input-pending/* [ Pass ]
 
 # Need to support 'direction: rtl' for scroll snap
 crbug.com/1012173 external/wpt/css/css-scroll-snap/snap-after-initial-layout/direction-rtl.html [ Failure ]

third_party/blink/web_tests/VirtualTestSuites

@@ -740,5 +740,12 @@
     "prefix": "bfcache-experiment-control",
     "bases": [ "http/tests/origin_trials/webexposed/bfcache-experiment-http-header-origin-trial.php" ],
     "args": [ "--enable-features=BackForwardCacheABExperimentControl" ]
+  },
+  {
+    "prefix": "threaded-composited-iframes",
+    "bases": ["external/wpt/is-input-pending"],
+    "args": ["--enable-threaded-compositing",
+             "--enable-features=CompositeCrossOriginIframes",
+             "--disable-auto-wpt-origin-isolation"]
   }
 ]

third_party/blink/web_tests/virtual/threaded-composited-iframes/external/wpt/is-input-pending/README.txt

+# This suite runs external/wpt/is-input-pending tests with threaded compositing
+# and layerized cross-origin iframes enabled (--enable-threaded-compositing flag,
+# the CompositeCrossOriginIframes feature).