Fix a bug in the benchmark script and enhance CSV output (#9955)

* Fix issue causing wasm to always be used even when useWasm = false

* Improve data quality of CSV output.

* pr comments

packages/devtools_app/benchmark/scripts/dart2wasm_performance_diff.dart

diff --git a/packages/devtools_app/benchmark/scripts/dart2wasm_performance_diff.dart b/packages/devtools_app/benchmark/scripts/dart2wasm_performance_diff.dart
index d0fb75c..8a8ba98 100644
--- a/packages/devtools_app/benchmark/scripts/dart2wasm_performance_diff.dart
+++ b/packages/devtools_app/benchmark/scripts/dart2wasm_performance_diff.dart
@@ -96,7 +96,7 @@
 
   void writeHeaders({required int averageOf}) {
     writeLines([
-      'Flutter DevTools performance benchmarks diff: dart2wasm diffed against dart2js.',
+      'Flutter DevTools performance benchmarks diff: dart2js (baseline) vs dart2wasm (test).',
       'Benchmark results were averaged over $averageOf benchmark run(s).',
       '',
       'These results were auto-generated by a script:',
@@ -105,9 +105,8 @@
     ]);
 
     // Write the Flutter and DevTools commit hash for the benchmark run.
-    // TODO(kenz): automatically detect these and write them to the CSV.
-    const flutter = '<enter manually by running \'flutter --version\'>';
-    const devtools = '<enter manually by running \'git log\'>';
+    final flutter = _detectFlutterVersion();
+    final devtools = _detectDevToolsCommit();
     writeLines([
       'Version info:',
       'Flutter: $flutter',
@@ -120,7 +119,8 @@
     writeLine([
       'Benchmark Name',
       'Metric',
-      'Value (micros)',
+      'Baseline (micros)',
+      'Test (micros)',
       'Delta (micros)',
       'Delta (%)',
     ]);
@@ -178,6 +178,49 @@
         '(Google Sheets, Excel, etc.) for viewing.',
       );
   }
+
+  String _detectFlutterVersion() {
+    try {
+      final result = Process.runSync('flutter', [
+        '--version',
+        '--machine',
+      ], runInShell: true);
+      if (result.exitCode == 0) {
+        final json =
+            jsonDecode(result.stdout.toString()) as Map<String, Object?>;
+        final flutterVersion = json['flutterVersion'];
+        final frameworkRevision = json['frameworkRevision'];
+        if (flutterVersion != null && frameworkRevision != null) {
+          return '$flutterVersion (revision $frameworkRevision)';
+        }
+        return result.stdout.toString().trim();
+      }
+    } catch (_) {}
+
+    try {
+      final result = Process.runSync('flutter', [
+        '--version',
+      ], runInShell: true);
+      if (result.exitCode == 0) {
+        return result.stdout.toString().trim().split('\n').first;
+      }
+    } catch (_) {}
+
+    return '<unknown>';
+  }
+
+  String _detectDevToolsCommit() {
+    try {
+      final result = Process.runSync('git', [
+        'rev-parse',
+        'HEAD',
+      ], runInShell: true);
+      if (result.exitCode == 0) {
+        return result.stdout.toString().trim();
+      }
+    } catch (_) {}
+    return '<unknown>';
+  }
 }
 
 Future<BenchmarkResults> runBenchmarkOrUseExisting(

packages/devtools_app/benchmark/scripts/utils.dart

diff --git a/packages/devtools_app/benchmark/scripts/utils.dart b/packages/devtools_app/benchmark/scripts/utils.dart
index 6d7f24e..cb557c5 100644
--- a/packages/devtools_app/benchmark/scripts/utils.dart
+++ b/packages/devtools_app/benchmark/scripts/utils.dart
@@ -45,14 +45,22 @@
 
 extension BenchmarkScoreExtension on BenchmarkScore {
   List<String> toCsvLine() {
+    final deltaValue = delta;
+    final baselineValue = deltaValue != null ? value - deltaValue : null;
+    final String deltaPercent;
+    if (baselineValue == null) {
+      deltaPercent = '';
+    } else if (baselineValue == 0) {
+      deltaPercent = 'N/A';
+    } else {
+      deltaPercent = (deltaValue! / baselineValue).toString();
+    }
     return [
       metric, // Metric name
-      value.toString(), // Value
-      delta?.toString() ?? '', // Delta value
-      // value - delta represents the baseline score.
-      delta != null
-          ? (delta! / (value - delta!)).toString()
-          : '', // Delta % value
+      baselineValue?.toString() ?? '', // Baseline value
+      value.toString(), // Test value
+      deltaValue?.toString() ?? '', // Delta value
+      deltaPercent, // Delta % value
     ];
   }
 }

packages/devtools_app/benchmark/test_infra/common.dart

diff --git a/packages/devtools_app/benchmark/test_infra/common.dart b/packages/devtools_app/benchmark/test_infra/common.dart
index 32ab643..ec978f0 100644
--- a/packages/devtools_app/benchmark/test_infra/common.dart
+++ b/packages/devtools_app/benchmark/test_infra/common.dart
@@ -10,11 +10,9 @@
 /// found" in DevTools.
 const _benchmarkInitialPage = '';
 
-const _wasmQueryParameters = {'compiler': 'wasm'};
-
 String benchmarkPath({required bool useWasm}) => Uri(
   path: _benchmarkInitialPage,
-  queryParameters: useWasm ? _wasmQueryParameters : null,
+  queryParameters: {'compiler': useWasm ? 'wasm' : 'js'},
 ).toString();
 
 String generateBenchmarkEntryPoint({required bool useWasm}) {