Inject the dprChanged Stream from the constructor, instead of grabbin…

…g a static field directly.

lib/web_ui/lib/src/engine/view_embedder/dimensions_provider/custom_element_dimensions_provider.dart

@@ -6,14 +6,17 @@ import 'dart:async';
 
 import 'package:ui/src/engine/display.dart';
 import 'package:ui/src/engine/dom.dart';
-import 'package:ui/src/engine/view_embedder/display_dpr_stream.dart';
 import 'package:ui/src/engine/window.dart';
 import 'package:ui/ui.dart' as ui show Size;
 
 import 'dimensions_provider.dart';
 
 /// This class provides observable, real-time dimensions of a host element.
 ///
+/// This class needs a `Stream` of `devicePixelRatio` changes, like the one
+/// provided by [DisplayDprStream], because html resize observers do not report
+/// DPR changes.
+///
 /// All the measurements returned from this class are potentially *expensive*,
 /// and should be cached as needed. Every call to every method on this class
 /// WILL perform actual DOM measurements.
@@ -24,9 +27,11 @@ import 'dimensions_provider.dart';
 /// to be effective.
 class CustomElementDimensionsProvider extends DimensionsProvider {
   /// Creates a [CustomElementDimensionsProvider] from a [_hostElement].
-  CustomElementDimensionsProvider(this._hostElement) {
+  CustomElementDimensionsProvider(this._hostElement, {
+    Stream<double>? onDprChange,
+  }) {
     // Send a resize event when the page DPR changes.
-    _dprChangeStreamSubscription = DisplayDprStream.instance.dprChanged.listen((_) {
+    _dprChangeStreamSubscription = onDprChange?.listen((_) {
       _broadcastSize(null);
     });
 

lib/web_ui/lib/src/engine/view_embedder/dimensions_provider/dimensions_provider.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:meta/meta.dart';
 import 'package:ui/src/engine/dom.dart';
+import 'package:ui/src/engine/view_embedder/display_dpr_stream.dart';
 import 'package:ui/src/engine/window.dart';
 import 'package:ui/ui.dart' as ui show Size;
 
@@ -31,7 +32,10 @@ abstract class DimensionsProvider {
   /// Creates the appropriate DimensionsProvider depending on the incoming [hostElement].
   factory DimensionsProvider.create({DomElement? hostElement}) {
     if (hostElement != null) {
-      return CustomElementDimensionsProvider(hostElement);
+      return CustomElementDimensionsProvider(
+        hostElement,
+        onDprChange: DisplayDprStream.instance.dprChanged,
+      );
     } else {
       return FullPageDimensionsProvider();
     }

lib/web_ui/test/engine/view_embedder/dimensions_provider/custom_element_dimensions_provider_test.dart

@@ -132,24 +132,21 @@ void doTests() {
 
     test('funnels DPR change events too', () async {
       // Override the source of DPR events...
-      final DomEventTarget eventTarget = createDomElement('div');
-      DisplayDprStream.instance = DisplayDprStream(
-        EngineFlutterDisplay.instance,
-        overrides: DebugDisplayDprStreamOverrides(
-          getMediaQuery: (_) => eventTarget,
-        )
+      final StreamController<double> dprController =
+          StreamController<double>.broadcast();
+
+      // Inject the dprController stream into the CustomElementDimensionsProvider.
+      final CustomElementDimensionsProvider provider =
+          CustomElementDimensionsProvider(
+        sizeSource,
+        onDprChange: dprController.stream,
       );
-      final CustomElementDimensionsProvider provider = CustomElementDimensionsProvider(sizeSource);
 
-      // The size that will be emitted by the provider eventually
-      final Future<ui.Size?> newSize = provider.onResize.first;
-
-      // Set the mock DPR value
+      // Set and broadcast the mock DPR value
       EngineFlutterDisplay.instance.debugOverrideDevicePixelRatio(3.2);
-      // Simulate the mediaQuery change event from the browser
-      eventTarget.dispatchEvent(createDomEvent('Event', 'change'));
+      dprController.add(3.2);
 
-      expect(newSize, completes);
+      expect(provider.onResize.first, completes);
       expect(provider.computePhysicalSize(), const ui.Size(32, 32));
     });