ResizeObserver depth calculation isn't correct

[jdm]

Spec: https://drafts.csswg.org/resize-observer/#calculate-depth-for-node

Implementation:

servo/components/script/dom/resizeobserver.rs

Line 330 in 8557bf6

let depth = node.inclusive_ancestors_in_flat_tree().count() - 1;

This is almost correct, but I think the spec actually wants the inclusive ancestor path. The - 1 was attempting to give us the noninclusive ancestor path, and removing it allows /resize-observer/notify.html to run to completion.

[jdm]

--- a/components/script/dom/resizeobserver.rs
+++ b/components/script/dom/resizeobserver.rs
@@ -327,7 +338,7 @@ impl ResizeObservation {
 /// <https://drafts.csswg.org/resize-observer/#calculate-depth-for-node>
 fn calculate_depth_for_node(target: &Element) -> ResizeObservationDepth {
     let node = target.upcast::<Node>();
-    let depth = node.inclusive_ancestors_in_flat_tree().count() - 1;
+    let depth = node.inclusive_ancestors_in_flat_tree().count();
     ResizeObservationDepth(depth)
 }

[jdm]

  ▶ ERROR /resize-observer/notify.html
  │   → ResizeObserver loop completed with undelivered notifications.
  │
  │ :0:0
  │   ▶ PASS [expected NOTRUN] guard
  │   └ PASS [expected FAIL] test2: remove/appendChild trigger notification
  │   ▶ FAIL [expected PASS] test3: dimensions match
  │   │   → assert_equals: expected 20 but got 21
  │   │
  │   │ notify@http://web-platform.test:8000/resize-observer/notify.html:131:22
  │   │ _handleNotification/<@http://web-platform.test:8000/resize-observer/resources/resizeTestHelper.js:99:42
  │   │ Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:2869:25
  │   └ _handleNotification@http://web-platform.test:8000/resize-observer/resources/resizeTestHelper.js:97:23
  │   ▶ FAIL [expected PASS] test4: transform do not cause notifications
  │   │   → assert_unreached: transform must not trigger notifications Reached unreachable code
  │   │
  │   │ notify@http://web-platform.test:8000/resize-observer/notify.html:158:25
  │   │ _handleNotification/<@http://web-platform.test:8000/resize-observer/resources/resizeTestHelper.js:99:42
  │   │ Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:2869:25
  │   └ _handleNotification@http://web-platform.test:8000/resize-observer/resources/resizeTestHelper.js:97:23
  │   ▶ FAIL [expected PASS] test6: inline element notifies once with 0x0.
  │   │   → assert_equals: expected 0 but got 38
  │   │
  │   │ notify@http://web-platform.test:8000/resize-observer/notify.html:206:22
  │   │ _handleNotification/<@http://web-platform.test:8000/resize-observer/resources/resizeTestHelper.js:99:42
  │   │ Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:2869:25
  │   └ _handleNotification@http://web-platform.test:8000/resize-observer/resources/resizeTestHelper.js:97:23
  │   ▶ FAIL [expected PASS] test11: display:none element should be notified
  │   │   → assert_unreached: Timed out waiting for notification. (1000ms) Reached unreachable code
  │   │ FAIL [expected PASS] test12: element sized 0x0 should be notified
  │   │   → assert_unreached: Timed out waiting for notification. (1000ms) Reached unreachable code
  │   │
  │   │ _handleTimeout/</<@http://web-platform.test:8000/resize-observer/resources/resizeTestHelper.js:123:27
  │   │ Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:2869:25
  │   │ _handleTimeout/<@http://web-platform.test:8000/resize-observer/resources/resizeTestHelper.js:122:27
  │   │ Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:2869:25
  │   │ _handleTimeout@http://web-platform.test:8000/resize-observer/resources/resizeTestHelper.js:117:23
  │   │ Test.prototype.step_timeout/<@http://web-platform.test:8000/resources/testharness.js:2990:25
  │   │ Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:2869:25
  └   └ Test.prototype.step_func/<@http://web-platform.test:8000/resources/testharness.js:2916:35