Fix code_transformers to consider dart symlinks (typical in brew installations)

pkg/code_transformers/lib/src/dart_sdk.dart

Index: pkg/code_transformers/lib/src/dart_sdk.dart
diff --git a/pkg/code_transformers/lib/src/dart_sdk.dart b/pkg/code_transformers/lib/src/dart_sdk.dart
index 5dfcab848905e2668c682aa32832a07eab6477ae..77dd04c51db70da9921114c01ab52d8c146ba16d 100644
--- a/pkg/code_transformers/lib/src/dart_sdk.dart
+++ b/pkg/code_transformers/lib/src/dart_sdk.dart
@@ -23,18 +23,24 @@ String get dartSdkDirectory {
 
   bool isSdkDir(String dirname) =>
       new File(path.join(dirname, 'lib', '_internal', 'libraries.dart'))
-        .existsSync();
+      .existsSync();
 
-  if (path.split(Platform.executable).length == 1) {
+  String executable = Platform.executable;
+  if (path.split(executable).length == 1) {
     // TODO(blois): make this cross-platform.
     // HACK: A single part, hope it's on the path.
-    var result = Process.runSync('which', ['dart'],
-        stdoutEncoding: convert.UTF8);
-
-    var sdkDir = path.dirname(path.dirname(result.stdout));
+    executable = Process.runSync('which', ['dart'],
+        stdoutEncoding: convert.UTF8).stdout.trim();
+    // In case Dart is symlinked (e.g. homebrew on Mac) follow symbolic links.
+    var link = new Link(executable);
+    if (link.existsSync()) {
+      executable = link.resolveSymbolicLinksSync();
+    }
+    var sdkDir = path.dirname(path.dirname(executable));
     if (isSdkDir(sdkDir)) return sdkDir;
   }
-  var dartDir = path.dirname(path.absolute(Platform.executable));
+
+  var dartDir = path.dirname(path.absolute(executable));
   // If there's a sub-dir named dart-sdk then we're most likely executing from
   // a dart enlistment build directory.
   if (isSdkDir(path.join(dartDir, 'dart-sdk'))) {