Move dart2js from sdk/lib/_internal/compiler to pkg/compiler

tests/compiler/dart2js/source_map_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/implementation/dart2js.dart' as entry;
-import 'package:compiler/implementation/apiimpl.dart';
+import 'package:compiler/src/dart2js.dart' as entry;
+import 'package:compiler/src/apiimpl.dart';
 
 import 'source_map_validator_helper.dart';
 import 'compiler_alt.dart' as alt;
 
 void main() {
   entry.compileFunc = alt.compile;
 
   asyncTest(() => createTempDir().then((Directory tmpDir) {
     print(
         'Compiling tests/compiler/dart2js/source_map_validator_test_file.dart');
     Future result = entry.internalMain(
         ['tests/compiler/dart2js/source_map_validator_test_file.dart',
          '-o${tmpDir.path}/out.js',
          '--library-root=sdk']);
       return result.then((_) {
         Compiler compiler = alt.compiler;
         Uri uri =
             new Uri.file('${tmpDir.path}/out.js', windows: Platform.isWindows);
         validateSourceMap(uri, compiler);
 
         print("Deleting '${tmpDir.path}'.");
         tmpDir.deleteSync(recursive: true);
       });
   }));
 }