[canvaskit] fix text background, foreground, familyFallback; add style tests

Author: yjbanov

lib/web_ui/lib/src/engine/assets.dart

@@ -88,7 +88,16 @@ class AssetManagerException implements Exception {
 class WebOnlyMockAssetManager implements AssetManager {
   String defaultAssetsDir = '';
   String defaultAssetManifest = '{}';
-  String defaultFontManifest = '[]';
+  String defaultFontManifest = '''[
+   {
+      "family":"$_robotoFontFamily",
+      "fonts":[{"asset":"$_robotoTestFontUrl"}]
+   },
+   {
+      "family":"$_ahemFontFamily",
+      "fonts":[{"asset":"$_ahemFontUrl"}]
+   }
+  ]''';
 
   @override
   String get assetsDir => defaultAssetsDir;

lib/web_ui/lib/src/engine/canvaskit/font_fallbacks.dart

@@ -388,6 +388,9 @@ class _ResolvedNotoSubset {
   final List<CodeunitRange> ranges;
 
   _ResolvedNotoSubset(this.url, this.family, this.ranges);
+
+  @override
+  String toString() => '_ResolvedNotoSubset($family, $url)';
 }
 
 _NotoFont _notoSansSC = _NotoFont('Noto Sans SC', <CodeunitRange>[
@@ -660,21 +663,64 @@ class FallbackFontDownloadQueue {
 }
 
 class NotoDownloader {
+  int _debugActiveDownloadCount = 0;
+
+  /// Returns a future that resolves when there are no pending downloads.
+  ///
+  /// Useful in tests to make sure that fonts are loaded before working with
+  /// text.
+  Future<void> debugWhenIdle() async {
+    if (assertionsEnabled) {
+      // Some downloads begin asynchronously in a microtask or in a Timer.run.
+      // Let those run before waiting for downloads to finish.
+      await Future<void>.delayed(Duration.zero);
+      while (_debugActiveDownloadCount > 0) {
+        await Future<void>.delayed(const Duration(milliseconds: 100));
+        // If we started with a non-zero count and hit zero while waiting, wait a
+        // little more to make sure another download doesn't get chained after
+        // the last one (e.g. font file download after font CSS download).
+        if (_debugActiveDownloadCount == 0) {
+          await Future<void>.delayed(const Duration(milliseconds: 100));
+        }
+      }
+    } else {
+      throw UnimplementedError();
+    }
+  }
+
   /// Downloads the [url] and returns it as a [ByteBuffer].
   ///
   /// Override this for testing.
   Future<ByteBuffer> downloadAsBytes(String url) {
-    return html.window.fetch(url).then((dynamic fetchResult) => fetchResult
+    if (assertionsEnabled) {
+      _debugActiveDownloadCount += 1;
+    }
+    final Future<ByteBuffer> result = html.window.fetch(url).then((dynamic fetchResult) => fetchResult
         .arrayBuffer()
         .then<ByteBuffer>((dynamic x) => x as ByteBuffer));
+    if (assertionsEnabled) {
+      result.whenComplete(() {
+        _debugActiveDownloadCount -= 1;
+      });
+    }
+    return result;
   }
 
   /// Downloads the [url] and returns is as a [String].
   ///
   /// Override this for testing.
   Future<String> downloadAsString(String url) {
-    return html.window.fetch(url).then((dynamic response) =>
+    if (assertionsEnabled) {
+      _debugActiveDownloadCount += 1;
+    }
+    final Future<String> result = html.window.fetch(url).then((dynamic response) =>
         response.text().then<String>((dynamic x) => x as String));
+    if (assertionsEnabled) {
+      result.whenComplete(() {
+        _debugActiveDownloadCount -= 1;
+      });
+    }
+    return result;
   }
 }