Cleanup 1: split parts into their own libraries, remove unused imports

pkg/compiler/lib/src/ssa/codegen_helpers.dart

Index: pkg/compiler/lib/src/ssa/codegen_helpers.dart
diff --git a/pkg/compiler/lib/src/ssa/codegen_helpers.dart b/pkg/compiler/lib/src/ssa/codegen_helpers.dart
index bafa5606b22ac7a3d8757c18f5013465218829e3..a68f70b77b486af287b41ce664996b7ee1b464cb 100644
--- a/pkg/compiler/lib/src/ssa/codegen_helpers.dart
+++ b/pkg/compiler/lib/src/ssa/codegen_helpers.dart
@@ -2,7 +2,14 @@
 // 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.
 
-part of ssa;
+import '../compiler.dart' show Compiler;
+import '../constants/values.dart';
+import '../elements/elements.dart';
+import '../js_backend/js_backend.dart';
+import '../types/types.dart';
+import '../universe/selector.dart' show Selector;
+
+import 'nodes.dart';
 
 /**
  * Replaces some instructions with specialized versions to make codegen easier.