Implement Chrome JS coverage

dwds/lib/dwds.dart

@@ -3,16 +3,20 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:convert';
 
 import 'package:build_daemon/data/build_status.dart';
+import 'package:dwds/src/debugging/webkit_debugger.dart';
 import 'package:dwds/src/utilities/shared.dart';
+import 'package:http/http.dart' as http;
 import 'package:logging/logging.dart';
 import 'package:meta/meta.dart';
 import 'package:shelf/shelf.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
 import 'src/connections/app_connection.dart';
 import 'src/connections/debug_connection.dart';
+import 'src/debugging/sources.dart';
 import 'src/handlers/asset_handler.dart';
 import 'src/handlers/dev_handler.dart';
 import 'src/handlers/injected_handler.dart';
@@ -125,3 +129,34 @@ class Dwds {
     );
   }
 }
+
+class Coverage {
+  LogWriter _logWriter;
+  Sources _sources;
+
+  Coverage(this._logWriter, this._sources);
+
+  Future start() async {
+    return await _sources.startPreciseCoverage();
+  }
+
+  Future collect() {
+    return _sources.takePreciseCoverage();
+  }
+
+  static Future<Coverage> init(LogWriter logWriter, String chromeUrl, int assetServerPort, String target, String applicationHost, int applicationPort) async {
+    final assetHandler = AssetHandler(assetServerPort, target, applicationHost, applicationPort);
+
+    // set up debugger connection
+    final response = await http.get(chromeUrl + '/json');
+    final url = jsonDecode(response.body)[0]['webSocketDebuggerUrl'] as String;
+
+    final wipConnection = await WipConnection.connect(url);
+    final wipDebugger = WipDebugger(wipConnection);
+    final remoteDebugger = WebkitDebugger(wipDebugger);
+
+    final sources = Sources(assetHandler, remoteDebugger, logWriter);
+
+    return Coverage(logWriter, sources);
+  }
+}

dwds/lib/src/debugging/sources.dart

@@ -39,6 +39,9 @@ class Sources {
   /// Paths to black box in the Chrome debugger.
   final _pathsToBlackBox = {'/packages/stack_trace/'};
 
+  /// Determines whether or not we've already enabled the profile
+  bool _profilerEnabled = false;
+
   /// Use `_readAssetOrNull` instead of using this directly, as it handles
   /// logging unsuccessful responses.
   final AssetHandler _assetHandler;
@@ -127,6 +130,26 @@ class Sources {
     return tokenPosTable;
   }
 
+  Future startProfiler() async {
+    if (_profilerEnabled) {
+      return;
+    }
+    _profilerEnabled = true;
+    await _remoteDebugger.sendCommand('Profiler.enable');
+  }
+
+  Future startPreciseCoverage() async {
+    await startProfiler();
+    await _remoteDebugger.sendCommand('Profiler.startPreciseCoverage');
+  }
+
+  Future takePreciseCoverage() async {
+    await startProfiler();
+    final rawCoverage = await _remoteDebugger.sendCommand('Profiler.takePreciseCoverage');
+    final jsCoverage = rawCoverage.result;
+    print('JS Coverage: $jsCoverage');
+  }
+
   void _clearCacheFor(WipScript script) {
     var serverPaths = _sourceToServerPaths[script.url] ?? {};
     for (var serverPath in serverPaths) {