Fix analyzer error

pkg/dev_compiler/lib/src/analyzer/context.dart

Index: pkg/dev_compiler/lib/src/analyzer/context.dart
diff --git a/pkg/dev_compiler/lib/src/analyzer/context.dart b/pkg/dev_compiler/lib/src/analyzer/context.dart
index 6dd239db74bdd7acff0c457ba6a62fbe3a6bfd83..bc47716a6446c1650d642aa64ec50b227b638527 100644
--- a/pkg/dev_compiler/lib/src/analyzer/context.dart
+++ b/pkg/dev_compiler/lib/src/analyzer/context.dart
@@ -51,6 +51,7 @@ class AnalyzerOptions {
       String dartSdkPath,
       this.dartSdkSummaryPath,
       this.customUrlMappings: const {},
+      this.packageRoot: null,

[Jennifer Messerly, 2016/09/28 17:49:05]

style nit: ": null" part is not needed.

you do need "this.packageRoot," though :)

       this.packagePaths: const []})
       : dartSdkPath = dartSdkPath ?? getSdkDir().path;