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

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

Index: pkg/compiler/lib/src/native/ssa.dart
diff --git a/pkg/compiler/lib/src/native/ssa.dart b/pkg/compiler/lib/src/native/ssa.dart
index b51c64d3bb477230981958953f271bb8ead18334..7555590c405a082981f75b412a003ab72380d9df 100644
--- a/pkg/compiler/lib/src/native/ssa.dart
+++ b/pkg/compiler/lib/src/native/ssa.dart
@@ -2,7 +2,25 @@
 // 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 native;
+import '../common.dart';
+import '../compiler.dart' show
+    Compiler;
+import '../constants/values.dart';
+import '../dart_types.dart';
+import '../elements/elements.dart';
+import '../js/js.dart' as js;
+import '../js_backend/js_backend.dart';
+import '../js_emitter/js_emitter.dart' show
+    CodeEmitterTask,
+    NativeEmitter;
+import '../ssa/builder.dart' show SsaBuilder;
+import '../ssa/nodes.dart' show
+    HInstruction,
+    HForeignCode,
+    HReturn;
+import '../tree/tree.dart';
+import '../universe/side_effects.dart' show
+    SideEffects;
 
 final RegExp nativeRedirectionRegExp = new RegExp(r'^[a-zA-Z][a-zA-Z_$0-9]*$');