Look for dart-sdk in two places.

pkg/analyzer-experimental/lib/src/generated/java_io.dart

 library java.io;
 
 import "dart:io";
 import "dart:uri";
 
 class JavaSystemIO {
   static Map<String, String> _properties = new Map();
   static String getProperty(String name) {
     {
       String value = _properties[name];
       if (value != null) {
         return value;
       }
     }
     if (name == 'os.name') {
       return Platform.operatingSystem;
     }
     if (name == 'line.separator') {
       if (Platform.operatingSystem == 'windows') {
         return '\r\n';
       }
       return '\n';
     }
     if (name == 'com.google.dart.sdk') {
       String exec = new Options().executable;
       if (exec.length != 0) {
-        String sdkPath = new Path(exec).directoryPath.directoryPath.toString();
+        String sdkPath;
+        // may be "xcodebuild/ReleaseIA32/dart" with "dart-sdk" sibling
+        {
+          sdkPath = new Path(exec).directoryPath.append("dart-sdk").toNativePath();
+          if (new Directory(sdkPath).existsSync()) {
+            _properties[name] = sdkPath;
+            return sdkPath;
+          }
+        }
+        // probably be "dart-sdk/bin/dart"
+        sdkPath = new Path(exec).directoryPath.directoryPath.toString();
         _properties[name] = sdkPath;
         return sdkPath;
       }
     }
     return null;
   }
   static String setProperty(String name, String value) {
     String oldValue = _properties[name];
     _properties[name] = value;
     return oldValue;
@@ skipping 32 matching lines @@
       return true;
     }
     return false;
   }
   Uri toURI() => new Uri.fromComponents(path: _path.toString());
   String readAsStringSync() => _newFile().readAsStringSync();
   int lastModified() => _newFile().lastModifiedSync().millisecondsSinceEpoch;
   File _newFile() => new File.fromPath(_path);
   Directory _newDirectory() => new Directory.fromPath(_path);
 }