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

tests/compiler/dart2js/source_mapping_test.dart

Index: tests/compiler/dart2js/source_mapping_test.dart
diff --git a/tests/compiler/dart2js/source_mapping_test.dart b/tests/compiler/dart2js/source_mapping_test.dart
index 23bb25119d13e81dda7a288fac85c3490ce9a27c..e1f73c09f1acb10cba09ae0e6f47baf1c83847d3 100644
--- a/tests/compiler/dart2js/source_mapping_test.dart
+++ b/tests/compiler/dart2js/source_mapping_test.dart
@@ -5,10 +5,10 @@
 import 'dart:async';
 import "package:expect/expect.dart";
 import "package:async_helper/async_helper.dart";
-import "package:compiler/src/dart2jslib.dart";
-import 'package:compiler/src/source_file.dart';
+import "package:compiler/implementation/dart2jslib.dart";
+import 'package:compiler/implementation/source_file.dart';
 import "mock_compiler.dart";
-import 'package:compiler/src/js_backend/js_backend.dart';
+import 'package:compiler/implementation/js_backend/js_backend.dart';
 
 Future<CodeBuffer> compileAll(SourceFile sourceFile) {
   MockCompiler compiler = new MockCompiler.internal();