Automated g4 rollback of changelist 243324798.

*** Reason for rollback ***

Breaks internal project tests

*** Original change description ***

In accordance with DeferredContentAware best practices

***

PiperOrigin-RevId: 243398462

Author: Googler

angular_components/lib/material_expansionpanel/material_expansionpanel.dart

@@ -20,7 +20,6 @@ import 'package:angular_components/model/action/async_action.dart';
 import 'package:angular_components/model/observable/observable.dart';
 import 'package:angular_components/utils/angular/id/id.dart';
 import 'package:angular_components/utils/browser/dom_service/dom_service.dart';
-import 'package:angular_components/utils/disposer/disposable_callback.dart';
 import 'package:angular_components/utils/disposer/disposer.dart';
 
 /// A material-styled expansion-panel.
@@ -138,28 +137,10 @@ class MaterialExpansionPanel
   @ViewChild('mainPanel')
   set mainPanel(HtmlElement mainPanel) {
     _mainPanel = mainPanel;
-
-    final transitionCheck = DisposableCallback(() {
-      // If we have a transition, turn off deferred content when it finishes
-      // closing. If we don't (because style mixins/overrides/disabled in tests)
-      // just forward the isExpanded change event.
-      if (_mainPanelHasHeightTransition) {
-        _disposer.addStreamSubscription(_mainPanel.onTransitionEnd.listen((_) {
-          // Clear height override so it will match the active child's height.
-          _mainPanel.style.height = '';
-          // If we just finished closing, let deferred content stop rendering
-          // the panel body.
-          if (!isExpanded) _contentVisible.add(false);
-        }));
-      } else {
-        _disposer.addStreamSubscription(isExpandedChange.listen((expanded) {
-          // Just check for false (closed). Open (true) is always done first.
-          if (!expanded) _contentVisible.add(false);
-        }));
-      }
-    });
-    _domService.scheduleRead(transitionCheck);
-    _disposer.addDisposable(transitionCheck);
+    _disposer.addStreamSubscription(_mainPanel.onTransitionEnd.listen((_) {
+      // Clear height override so it will match the active child's height.
+      _mainPanel.style.height = '';
+    }));
   }
 
   HtmlElement _headerPanel;
@@ -238,8 +219,7 @@ class MaterialExpansionPanel
       StreamController<bool>.broadcast(sync: true);
 
   @override
-  Stream<bool> get contentVisible => _contentVisible.stream;
-  final _contentVisible = StreamController<bool>.broadcast(sync: true);
+  Stream<bool> get contentVisible => isExpandedChange;
 
   /// Whether a different panel in the set is currently expanded.
   ///
@@ -542,11 +522,7 @@ class MaterialExpansionPanel
     stream.add(actionCtrl.action);
     var stateWasInitialized = initialized;
     actionCtrl.execute(() {
-      // Update our state before redrawing. State changes need to occur before
-      // follow ups (animation or autofocus) so that styles and deferred content
-      // can update.
       _isExpanded.value = expand;
-      if (expand) _contentVisible.add(true);
       if (byUserAction) _isExpandedChangeByUserAction.add(expand);
       _changeDetector.markForCheck();
       if (expand && _focusableItem != null) {
@@ -617,9 +593,10 @@ class MaterialExpansionPanel
     final contentHeight = _mainContent.scrollHeight;
     var expandedPanelHeight = '';
 
+    final mainPanelStyle = _mainPanel.getComputedStyle();
     // Do our best to make sure that onTransitionEnd will fire later.
     final hasHeightTransition =
-        contentHeight > 0 && _mainPanelHasHeightTransition;
+        contentHeight > 0 && mainPanelStyle.transition.contains('height');
 
     if (hasHeightTransition) {
       // If the content-wrapper has a top margin, it is not reflected in the
@@ -630,12 +607,6 @@ class MaterialExpansionPanel
     return expandedPanelHeight;
   }
 
-  bool get _mainPanelHasHeightTransition {
-    final mainPanelStyle = _mainPanel.getComputedStyle();
-    // Do our best to make sure that onTransitionEnd will fire later.
-    return mainPanelStyle.transition.contains('height');
-  }
-
   /// Reads the DOM state to calculate the height of the header in its
   /// current condition.
   ///

angular_components/lib/material_expansionpanel/material_expansionpanel.html

@@ -54,7 +54,7 @@
 
 <!-- Expanded section -->
 <main [class.hidden]="!isExpanded" #mainPanel role="presentation" autoId #mainId="autoId">
-  <div #mainContent *deferredContent="forceContent: forceContentWhenClosed">
+  <div #mainContent *deferredContent="true;forceContent: forceContentWhenClosed">
     <div #contentWrapper class="content-wrapper" [class.hidden-header]="hideExpandedHeader">
       <material-icon
           *ngIf="shouldShowHiddenHeaderExpandIcon && shouldExpandOnLeft"

angular_components/lib/material_expansionpanel/material_expansionpanel.scss

@@ -58,30 +58,18 @@
   }
 }
 
-// It is impossible to change 'just' the transition function for visibility in hte hidden style,
-// so use a mixin to keep everything consistent except that.
-@mixin header-transition($visibility_function) {
-  transition: height $mat-transition $mat-transition-standard,
-  min-height $mat-transition $mat-transition-standard,
-  opacity $mat-transition-slow $mat-transition-standard,
-  visibility $mat-transition-slow $visibility_function;
-}
-
 header {
   display: flex;
   color: $mat-transparent-black;
-  // When switching to expanded, turn visibility on at the start.
-  @include header-transition(step-start);
-  visibility: inherit;
+  transition: height $mat-transition $mat-transition-standard,
+              min-height $mat-transition $mat-transition-standard,
+              opacity $mat-transition-slow $mat-transition-standard;
 
   &.hidden {
     min-height: 0;
     height: 0;
     opacity: 0;
     overflow: hidden;
-    // When switching to hidden, don't turn off visibility until the end.
-    @include header-transition(step-end);
-    visibility: hidden;
   }
 }
 
@@ -144,29 +132,17 @@ header {
   padding-right: $mat-grid * 2;
 }
 
-// It is impossible to change 'just' the transition function for visibility in hte hidden style,
-// so use a mixin to keep everything consistent except that.
-@mixin main-transition($visibility-function) {
-  transition: height $mat-transition $mat-transition-standard,
-              opacity $mat-transition $mat-transition-standard,
-              visibility $mat-transition $visibility-function;
-}
-
 main {
   max-height: 100%;
   opacity: 1;
   overflow: hidden;
-  // When switching to expanded, turn visibility on at the start.
-  @include main-transition(step-start);
-  visibility: inherit;
+  transition: height $mat-transition $mat-transition-standard,
+              opacity $mat-transition $mat-transition-standard;
   width: 100%;
 
   &.hidden {
     height: 0;
     opacity: 0;
-    // When switching to hidden, don't turn off visibility until the end.
-    @include main-transition(step-end);
-    visibility: hidden;
   }
 }