Move common URIs to common/names.dart

pkg/compiler/lib/src/dart_backend/backend.dart

Index: pkg/compiler/lib/src/dart_backend/backend.dart
diff --git a/pkg/compiler/lib/src/dart_backend/backend.dart b/pkg/compiler/lib/src/dart_backend/backend.dart
index 1fbc6f40e746f6e3ab04a49cbc2e444ceb478416..20695ceffebc14c01d59cec4d939ddd3eb526578 100644
--- a/pkg/compiler/lib/src/dart_backend/backend.dart
+++ b/pkg/compiler/lib/src/dart_backend/backend.dart
@@ -230,10 +230,10 @@ class DartBackend extends Backend {
       }
     });
     if (useMirrorHelperLibrary &&
-        loadedLibraries.containsLibrary(Compiler.DART_MIRRORS)) {
+        loadedLibraries.containsLibrary(Uris.dart_mirrors)) {
       return compiler.libraryLoader.loadLibrary(
           compiler.translateResolvedUri(
-              loadedLibraries.getLibrary(Compiler.DART_MIRRORS),
+              loadedLibraries.getLibrary(Uris.dart_mirrors),
               MirrorRenamerImpl.DART_MIRROR_HELPER, null)).
           then((LibraryElement library) {
         mirrorRenamer = new MirrorRenamerImpl(compiler, this, library);