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

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

Index: pkg/compiler/lib/src/ssa/value_range_analyzer.dart
diff --git a/pkg/compiler/lib/src/ssa/value_range_analyzer.dart b/pkg/compiler/lib/src/ssa/value_range_analyzer.dart
index 7cd149e23d46e4ad90196b5362ba625f0ed963d4..22c127aead0a3aad5b8b4b44709f2c808df3a093 100644
--- a/pkg/compiler/lib/src/ssa/value_range_analyzer.dart
+++ b/pkg/compiler/lib/src/ssa/value_range_analyzer.dart
@@ -2,8 +2,15 @@
 // 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 '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
+import '../compiler.dart' show Compiler;
+import '../constant_system_dart.dart';
+import '../constants/constant_system.dart';
+import '../constants/values.dart';
+import '../js_backend/js_backend.dart';
+
+import 'nodes.dart';
+import 'optimize.dart';
 
 class ValueRangeInfo {
   final ConstantSystem constantSystem;