fixes detection of SDK libraries

lib/devc.dart

Index: lib/devc.dart
diff --git a/lib/devc.dart b/lib/devc.dart
index 4415f86c86f50a7733f52f41217b4d226bac6771..6972be3271ef332a40de810270fc26c5e2513689 100644
--- a/lib/devc.dart
+++ b/lib/devc.dart
@@ -155,7 +155,7 @@ class Compiler implements AbstractCompiler {
     context.applyChanges(new ChangeSet()..changedSource(source));
     var entryUnit = context.resolveCompilationUnit2(source, source);
     var lib = entryUnit.element.enclosingElement;
-    if (!options.checkSdk && lib.isInSdk) return;
+    if (!options.checkSdk && lib.source.uri.scheme == 'dart') return;

[vsm, 2015/06/10 16:41:15]

Move _isDartUri to utils and call that instead?

[Jennifer Messerly, 2015/06/10 16:46:04]

funny, almost did that. The thing is, now it becomes an opaque call, and instead
of a simple isInSdk, you have to import 'utils.dart' just do a URI scheme check.
Overall, I'd prefer to keep it as is ... it's kind of my informal rule of
"straightforward check of a single property" that should be inlined.

(Contrast with isInlineJS, that needs to check 3 things, two of them unrelated)

     var current = node.info;
     if (current != null) {
       assert(current.library == lib);