Add more descriptive error messages to TapToStopFling.html for better…

… debugging.

Also changed file name to conform to convention.

Change-Id: Ib901161728143882f0f2abdc01e79c03bdec7f6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6001495
Reviewed-by: Michal Mocny <mmocny@chromium.org>
Commit-Queue: Hao Liu <haoliuk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1379954}

event-timing/TapToStopFling.html → event-timing/tap-to-stop-fling.html

@@ -32,10 +32,12 @@
     assert_equals(entries.length, 2, "two pointerdown entries should be received");
     let entry = entries[0];
     assert_equals(entry.name, 'pointerdown');
-    assert_equals(entry.interactionId, 0);
+    assert_equals(entry.interactionId, 0, '1st pointerdown event should have a \
+    0 interaction id');
     entry = entries[1];
     assert_equals(entry.name, 'pointerdown');
-    assert_equals(entry.interactionId, 0);
+    assert_equals(entry.interactionId, 0, '2nd pointerdown event should have a \
+    0 interaction id');
   }
 
   promise_test(async t => {