Introduce "CommonElements"

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 ddc1eafc5bdd8f3360d77fa3f1fe779a175aba45..8c3594828609aba6b0ee7f03b59551239ae5ce8e 100644
--- a/tests/compiler/dart2js/minimal_resolution_test.dart
+++ b/tests/compiler/dart2js/minimal_resolution_test.dart
@@ -15,7 +15,7 @@ import 'memory_compiler.dart';
 main() {
   asyncTest(() async {
     await analyze('main() {}');
-    await analyze('main() => proxy;', proxyConstant: true);
+    await analyze('main() => proxy;', proxyConstantComputed: true);
     await analyze('@deprecated main() {}');
     await analyze('@deprecated main() => deprecated;', deprecatedClass: true);
     await analyze('main() => deprecated;', deprecatedClass: true);
@@ -34,18 +34,21 @@ void checkInstantiated(Compiler compiler, ClassElement cls, bool expected) {
 }
 
 analyze(String code,
-    {bool proxyConstant: false, bool deprecatedClass: false}) async {
+    {bool proxyConstantComputed: false, bool deprecatedClass: false}) async {
   CompilationResult result = await runCompiler(
       memorySourceFiles: {'main.dart': code}, options: ['--analyze-only']);
   Expect.isTrue(result.isSuccess);
   Compiler compiler = result.compiler;
-  Expect.equals(proxyConstant, compiler.resolution.proxyConstant != null,
+  Expect.equals(proxyConstantComputed,
+      compiler.resolution.wasProxyConstantComputedTestingOnly,
       "Unexpected computation of proxy constant.");
 
   checkInstantiated(
-      compiler, compiler.coreLibrary.find('_Proxy'), proxyConstant);
+      compiler, compiler.commonElements.coreLibrary.find('_Proxy'),
+      proxyConstantComputed);
   checkInstantiated(
-      compiler, compiler.coreLibrary.find('Deprecated'), deprecatedClass);
+      compiler, compiler.commonElements.coreLibrary.find('Deprecated'),
+      deprecatedClass);
 
   LibraryElement jsHelperLibrary =
       compiler.libraryLoader.lookupLibrary(BackendHelpers.DART_JS_HELPER);