Rename apiimpl.Compiler to CompilerImpl.

tests/compiler/dart2js/source_map_deferred_d2js_validity_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 'dart:io';
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/dart2js.dart' as entry;
 import 'package:compiler/src/apiimpl.dart';
 import 'package:compiler/compiler.dart';
 
 import 'source_map_validator_helper.dart';
 
 void main() {
   asyncTest(() => createTempDir().then((Directory tmpDir) {
     String file =
         'tests/compiler/dart2js/source_map_deferred_validator_test_file.dart';
     print("Compiling $file");
     Future result = entry.internalMain(
         [file,
          '-o${tmpDir.path}/out.js',
          '--library-root=sdk']);
       return result.then((CompilationResult result) {
-        Compiler compiler = result.compiler;
+        CompilerImpl compiler = result.compiler;
         Uri mainUri = new Uri.file('${tmpDir.path}/out.js',
                                    windows: Platform.isWindows);
         Uri deferredUri = new Uri.file('${tmpDir.path}/out.js_1.part.js',
                                        windows: Platform.isWindows);
         validateSourceMap(mainUri,
                           mainUri: Uri.base.resolve(file),
                           mainPosition: const Position(7, 1),
                           compiler: compiler);
         validateSourceMap(deferredUri,
                           compiler: compiler);
 
         print("Deleting '${tmpDir.path}'.");
         tmpDir.deleteSync(recursive: true);
       });
   }));
 }