Added a flag for enabling Dart Debug Extension backend. (#487)

* Added a flag for enabling Dart Debug Extension backend.

Author: Pi Songkuntham

webdev/lib/src/command/configuration.dart

@@ -10,6 +10,7 @@ import '../logging.dart';
 
 const autoOption = 'auto';
 const chromeDebugPortFlag = 'chrome-debug-port';
+const debugExtensionFlag = 'debug-extension';
 const debugFlag = 'debug';
 const hostnameFlag = 'hostname';
 const hotReloadFlag = 'hot-reload';
@@ -70,6 +71,7 @@ ReloadConfiguration _parseReloadConfiguration(ArgResults argResults) {
 class Configuration {
   final bool _autoRun;
   final int _chromeDebugPort;
+  final bool _debugExtension;
   final bool _debug;
   final String _hostname;
   final bool _launchInChrome;
@@ -85,6 +87,7 @@ class Configuration {
   Configuration({
     bool autoRun,
     int chromeDebugPort,
+    bool debugExtension,
     bool debug,
     String hostname,
     bool launchInChrome,
@@ -98,6 +101,7 @@ class Configuration {
     bool verbose,
   })  : _autoRun = autoRun,
         _chromeDebugPort = chromeDebugPort,
+        _debugExtension = debugExtension,
         _debug = debug,
         _hostname = hostname,
         _launchInChrome = launchInChrome,
@@ -113,6 +117,8 @@ class Configuration {
 
   int get chromeDebugPort => _chromeDebugPort ?? 0;
 
+  bool get debugExtension => _debugExtension ?? false;
+
   bool get debug => _debug ?? false;
 
   String get hostname => _hostname ?? 'localhost';
@@ -140,6 +146,10 @@ class Configuration {
         ? int.parse(argResults[chromeDebugPortFlag] as String)
         : defaultConfiguration.chromeDebugPort;
 
+    var debugExtension = argResults.options.contains(debugExtensionFlag)
+        ? argResults[debugExtensionFlag] as bool
+        : defaultConfiguration.debugExtension;
+
     var debug = argResults.options.contains(debugFlag)
         ? argResults[debugFlag] as bool
         : defaultConfiguration.debug;
@@ -199,6 +209,7 @@ class Configuration {
 
     return Configuration(
         chromeDebugPort: chromeDebugPort,
+        debugExtension: debugExtension,
         debug: debug,
         hostname: hostname,
         launchInChrome: launchInChrome,

webdev/lib/src/command/serve_command.dart

@@ -58,6 +58,8 @@ refresh: Performs a full page refresh.
     ..addFlag(debugFlag,
         help: 'Enable the launching of DevTools (Alt + D / Option + D). '
             'This also enables --$launchInChromeFlag.')
+    ..addFlag(debugExtensionFlag,
+        help: 'Enable the backend for the Dart Debug Extension.', hide: true)
     ..addSeparator('Advanced:')
     ..addOption(chromeDebugPortFlag,
         help: 'Specify which port the Chrome debugger is listening on. '