Flush styles when checking the play state of a CSSTransition.

Bug: 1006086
Change-Id: I7abf288db967ebb09a6a61be54fcbeaddab8febd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2091587
Commit-Queue: Kevin Ellis <kevers@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748214}

third_party/blink/renderer/core/animation/css/css_transition.cc

@@ -4,6 +4,8 @@
 
 #include "third_party/blink/renderer/core/animation/css/css_transition.h"
 
+#include "third_party/blink/renderer/core/dom/document.h"
+
 namespace blink {
 
 CSSTransition::CSSTransition(ExecutionContext* execution_context,
@@ -17,4 +19,12 @@ AtomicString CSSTransition::transitionProperty() const {
   return transition_property_.GetCSSPropertyName().ToAtomicString();
 }
 
+String CSSTransition::playState() const {
+  // TODO(1043778): Flush is likely not required once the CSSTransition is
+  // disassociated from its owning element.
+  if (GetDocument())
+    GetDocument()->UpdateStyleAndLayoutTree();
+  return Animation::playState();
+}
+
 }  // namespace blink

third_party/blink/renderer/core/animation/css/css_transition.h

@@ -26,6 +26,17 @@ class CORE_EXPORT CSSTransition : public Animation {
     return transition_property_.GetCSSProperty();
   }
 
+  // Animation overrides.
+  // Various operations may affect the computed values of properties on
+  // elements. User agents may, as an optimization, defer recomputing these
+  // values until it becomes necessary; however, all operations included in the
+  // programming interfaces defined in the web-animations and css-transitions
+  // specifications, must produce a result consistent with having fully
+  // processed any such pending changes to computed values.  Notably, setting
+  // display:none must update the play state.
+  // https://drafts.csswg.org/css-transitions-2/#requirements-on-pending-style-changes
+  String playState() const override;
+
  private:
   PropertyHandle transition_property_;
 };

third_party/blink/web_tests/external/wpt/css/css-transitions/CSSTransition-canceling.tentative-expected.txt

-This is a testharness.js-based test.
-PASS Animated style is cleared after canceling a running CSS transition
-PASS After canceling a transition, it can still be re-used
-PASS After canceling a finished transition, it can still be re-used
-PASS After canceling a transition, updating transition properties doesn't make it live again
-FAIL Setting display:none on an element cancels its transitions assert_equals: expected "idle" but got "running"
-FAIL Setting display:none cancels transitions on a child element assert_equals: expected "idle" but got "running"
-PASS Removing a property from transition-property cancels transitions on that property
-PASS Setting zero combined duration
-PASS Changing style to another interpolable value cancels the original transition
-PASS An after-change style value can't be interpolated
-PASS Reversing a running transition cancels the original transition
-Harness: the test ran to completion.
-