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

tests/compiler/dart2js/backend_dart/opt_shrinking_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 'sexpr_unstringifier.dart';
 import "package:expect/expect.dart";
-import 'package:compiler/src/cps_ir/cps_ir_nodes.dart';
-import 'package:compiler/src/cps_ir/cps_ir_nodes_sexpr.dart';
-import 'package:compiler/src/cps_ir/optimizers.dart';
+import 'package:compiler/implementation/cps_ir/cps_ir_nodes.dart';
+import 'package:compiler/implementation/cps_ir/cps_ir_nodes_sexpr.dart';
+import 'package:compiler/implementation/cps_ir/optimizers.dart';
 
 // The tests in this file that ensure shrinking reductions work as expected.
 // Reductions and their corresponding names are taken from
 // 'Compiling with Continuations, Continued' by Andrew Kennedy.
 
 // Basic dead-val: letprim x = V in K -> K (x not free in K).
 //
 //  int main() {
 //    int i = 42;
 //    return 0;
@@ skipping 208 matching lines @@
   testShrinkingReducer(ITERATIVE_DEAD_VAL1_IN, ITERATIVE_DEAD_VAL1_OUT);
   testShrinkingReducer(ITERATIVE_DEAD_VAL2_IN, ITERATIVE_DEAD_VAL2_OUT);
   testShrinkingReducer(DEAD_CONT_IN, DEAD_CONT_OUT);
   testShrinkingReducer(ITERATIVE_DEAD_CONT_IN, ITERATIVE_DEAD_CONT_OUT);
   testShrinkingReducer(BETA_CONT_LIN_IN, BETA_CONT_LIN_OUT);
   testShrinkingReducer(ARG_BETA_CONT_LIN_IN, ARG_BETA_CONT_LIN_OUT);
   testShrinkingReducer(RECURSIVE_BETA_CONT_LIN_IN, RECURSIVE_BETA_CONT_LIN_OUT);
   testShrinkingReducer(USED_BETA_CONT_LIN_IN, USED_BETA_CONT_LIN_OUT);
   testShrinkingReducer(ETA_CONT_IN, ETA_CONT_OUT);
 }