[Sheriff] Disable InputRouterImplTest.GestureTypesIgnoringAck on Fuchsia

It's been flaking heavily since
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Fuchsia%20x64/14471.

TBR=sahel@chromium.org

Bug: 866946
Change-Id: Iadbf5f330b9775d10dc5969d36f3fef8ad19a205
Reviewed-on: https://chromium-review.googlesource.com/1148597Reviewed-by: Derek Cheng <imcheng@chromium.org>
Commit-Queue: Derek Cheng <imcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577596}

content/browser/renderer_host/input/input_router_impl_unittest.cc

@@ -767,7 +767,13 @@ TEST_F(InputRouterImplTest, TouchTypesIgnoringAck) {
   EXPECT_FALSE(HasPendingEvents());
 }
 
-TEST_F(InputRouterImplTest, GestureTypesIgnoringAck) {
+// TODO(https://crbug.com/866946): Test is flaky on Fuchsia.
+#if defined(OS_FUCHSIA)
+#define MAYBE_GestureTypesIgnoringAck DISABLED_GestureTypesIgnoringAck
+#else
+#define MAYBE_GestureTypesIgnoringAck GestureTypesIgnoringAck
+#endif
+TEST_F(InputRouterImplTest, MAYBE_GestureTypesIgnoringAck) {
   // We test every gesture type, ensuring that the stream of gestures is valid.
   const WebInputEvent::Type eventTypes[] = {
       WebInputEvent::kGestureTapDown,     WebInputEvent::kGestureShowPress,