Update imports to use package:compiler and package:try.

dart/tests/compiler/dart2js/source_mapping_test.dart

Index: dart/tests/compiler/dart2js/source_mapping_test.dart
diff --git a/dart/tests/compiler/dart2js/source_mapping_test.dart b/dart/tests/compiler/dart2js/source_mapping_test.dart
index 8bc38b7175f097cb1ddc5e5fcf2e87c5aa95c8e7..3118cd3d8e57feab8d2e13b350a6813e5714e145 100644
--- a/dart/tests/compiler/dart2js/source_mapping_test.dart
+++ b/dart/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 "../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart";
-import '../../../sdk/lib/_internal/compiler/implementation/source_file.dart';
+import "package:compiler/implementation/dart2jslib.dart";
+import 'package:compiler/implementation/source_file.dart';
 import "mock_compiler.dart";
-import '../../../sdk/lib/_internal/compiler/implementation/js_backend/js_backend.dart';
+import 'package:compiler/implementation/js_backend/js_backend.dart';
 
 Future<CodeBuffer> compileAll(SourceFile sourceFile) {
   MockCompiler compiler = new MockCompiler.internal();