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

tests/compiler/dart2js/deferred_mirrors_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.
 
 // Test of the graph segmentation algorithm used by deferred loading
 // to determine which elements can be deferred and which libraries
 // much be included in the initial download (loaded eagerly).
 
 import 'package:expect/expect.dart';
 import "package:async_helper/async_helper.dart";
 import 'memory_source_file_helper.dart';
 import "memory_compiler.dart";
 
-import 'package:compiler/src/dart2jslib.dart'
+import 'package:compiler/implementation/dart2jslib.dart'
        as dart2js;
 
 runTest(String mainScript, test) {
   Compiler compiler = compilerFor(MEMORY_SOURCE_FILES,
       outputProvider: new OutputCollector());
   asyncTest(() => compiler.run(Uri.parse(mainScript))
       .then((_) => test(compiler)));
 }
 
 lookupLibrary(compiler, name) {
@@ skipping 165 matching lines @@
 library lib5;
 
 foo() {}
 """,
 "lib6.dart": """
 library lib6;
 
 foo() {}
 """,
 };