feat(dart): Use ts2dart for transpilation in Karma Dart.

tools/transpiler/karma-ts2dart-preprocessor.js

@@ -0,0 +1,35 @@
+// Transpiles JavaScript and TypeScript code to Dart using ts2dart.
+
+var ts2dart = require('ts2dart');
+var rundartpackage = require('../build/rundartpackage.js');
+
+module.exports = {
+  'preprocessor:ts2dart': ['factory', createTs2DartPreprocessor]
+};
+
+function createTs2DartPreprocessor(logger, basePath, config, emitter) {
+  var log = logger.create('ts2dart');
+  return function(content, file, done) {
+    try {
+      var moduleName = config.resolveModuleName(file.originalPath);
+      file.path = config.transformPath(file.originalPath);
+      var transpiler = new ts2dart.Transpiler();
+      var transpiledContent = transpiler.translateFile(file.originalPath, moduleName);
+      // TODO(martinprobst): Source maps.
+      done(null, transpiledContent);
+    } catch (errors) {
+      var errorString;
+      if (errors.forEach) {
+        errors.forEach(function(error) { log.error(error); });
+        errorString = errors.join('\n');
+      } else {
+        log.error(errors);
+        errorString = errors;
+      }
+      done(new Error('ts2dart compile errors:\n' + errorString));
+    }
+  };
+}
+
+createTs2DartPreprocessor
+    .$inject = ['logger', 'config.basePath', 'config.ts2dartPreprocessor', 'emitter'];