Disable dependency_grapher_test on dart2js for now.

The test has a transitive dependency on dart:io which I haven't quite
figured out yet.  Once I figure out how to remove the transitive
dependency I'll re-enable the test.

TBR=sigmund@google.com

Review-Url: https://codereview.chromium.org/2582733003 .
diff --git a/pkg/pkg.status b/pkg/pkg.status
index 616f732..0f28f5a 100644
--- a/pkg/pkg.status
+++ b/pkg/pkg.status
@@ -67,6 +67,7 @@
 front_end/test/memory_file_system_test: CompileTimeError # Issue 23773
 front_end/test/physical_file_system_test: SkipByDesign # Uses dart:io
 front_end/test/src/base/libraries_reader_test: SkipByDesign # Uses dart:io
+front_end/test/dependency_grapher_test: SkipByDesign # Uses dart:io
 
 [ $compiler == dart2js && $fast_startup ]
 front_end/test/*: SkipByDesign # Tests written with dart:mirrors.