Serve dart2wasm source map files (#2532)

Author: osa1

pkgs/test/CHANGELOG.md

@@ -3,6 +3,7 @@
 * Restrict to latest version of analyzer package.
 * Require Dart 3.7
 * Add `--coverage-path` and `--branch-coverage` options to `dart test`.
+* Serve dart2wasm source map files.
 
 ## 1.26.3
 

pkgs/test/lib/src/runner/browser/compilers/dart2wasm.dart

@@ -134,6 +134,7 @@ class Dart2WasmSupport extends CompilerSupport with WasmHtmlWrapper {
       var baseUrl =
           '${p.toUri(p.relative(dartPath, from: _root)).path}.browser_test.dart';
       var wasmUrl = '$baseUrl.wasm';
+      var sourceMapUrl = '$wasmUrl.map';
       var jsRuntimeWrapperUrl = '$baseUrl.js';
       var jsRuntimeUrl = '$baseUrl.mjs';
       var htmlUrl = '$baseUrl.html';
@@ -186,6 +187,14 @@ class Dart2WasmSupport extends CompilerSupport with WasmHtmlWrapper {
           headers: {'Content-Type': 'text/html'},
         );
       });
+
+      var sourceMapPath = '$wasmPath.map';
+      _pathHandler.add(sourceMapUrl, (request) {
+        return shelf.Response.ok(
+          File(sourceMapPath).readAsBytesSync(),
+          headers: {'Content-Type': 'application/json'},
+        );
+      });
     });
   }