Rename apiimpl.Compiler to CompilerImpl.

tests/compiler/dart2js/check_elements_invariants_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/apiimpl.dart';
 import 'package:expect/expect.dart';
 import 'package:compiler/src/elements/elements.dart'
     show ClassElement;
 import 'package:compiler/src/resolution/class_members.dart'
     show ClassMemberMixin;
 import 'memory_compiler.dart';
 
 
 const String DART2JS_SOURCE =
     'pkg/compiler/lib/src/dart2js.dart';
 const List<String> DART2JS_OPTIONS = const <String>[
       '--categories=Client,Server',
       '--disable-type-inference'
     ];
 
-Iterable<ClassElement> computeLiveClasses(Compiler compiler) {
+Iterable<ClassElement> computeLiveClasses(CompilerImpl compiler) {
   return new Set<ClassElement>()
       ..addAll(compiler.resolverWorld.directlyInstantiatedClasses)
       ..addAll(compiler.codegenWorld.directlyInstantiatedClasses);
 }
 
 void checkClassInvariants(ClassElement cls) {
   ClassMemberMixin impl = cls;
   Expect.isTrue(impl.areAllMembersComputed(),
       "Not all members have been computed for $cls.");
 }
 
 Future checkElementInvariantsAfterCompiling(Uri uri) async {
   CompilationResult result =
       await runCompiler(entryPoint: uri, options: DART2JS_OPTIONS);
   Expect.isTrue(result.isSuccess, "Compilation of dart2js failed.");
 
   computeLiveClasses(result.compiler).forEach(checkClassInvariants);
 }
 
 void main () {
   var uri = Uri.base.resolve(DART2JS_SOURCE);
   asyncTest(() => checkElementInvariantsAfterCompiling(uri));
 }