Use entities in CommonElements interface.

tests/compiler/dart2js/minimal_resolution_test.dart

Index: tests/compiler/dart2js/minimal_resolution_test.dart
diff --git a/tests/compiler/dart2js/minimal_resolution_test.dart b/tests/compiler/dart2js/minimal_resolution_test.dart
index 14dec299267800827d7698fa1361e3227f39642a..a267acc81dea03f745c0b242c8c7357a81bc1289 100644
--- a/tests/compiler/dart2js/minimal_resolution_test.dart
+++ b/tests/compiler/dart2js/minimal_resolution_test.dart
@@ -44,12 +44,10 @@ analyze(String code,
       compiler.resolution.wasProxyConstantComputedTestingOnly,
       "Unexpected computation of proxy constant.");
 
+  LibraryElement coreLibrary = compiler.commonElements.coreLibrary;
   checkInstantiated(
-      compiler,
-      compiler.commonElements.coreLibrary.find('_Proxy'),
-      proxyConstantComputed);
-  checkInstantiated(compiler,
-      compiler.commonElements.coreLibrary.find('Deprecated'), deprecatedClass);
+      compiler, coreLibrary.find('_Proxy'), proxyConstantComputed);
+  checkInstantiated(compiler, coreLibrary.find('Deprecated'), deprecatedClass);
 
   LibraryElement jsHelperLibrary =
       compiler.libraryLoader.lookupLibrary(BackendHelpers.DART_JS_HELPER);