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

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

 // Copyright (c) 2013, 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.
 
 library dart2js.ir_builder_task;
 
 import '../closure.dart' as closure;
 import '../common.dart';
 import '../common/names.dart' show
     Identifiers,
@@ skipping 30 matching lines @@
 import '../constants/values.dart' show
     ConstantValue;
 import 'cps_ir_nodes.dart' as ir;
 import 'cps_ir_builder.dart';
 import '../native/native.dart' show
     NativeBehavior,
     HasCapturedPlaceholders;
 
 // TODO(karlklose): remove.
 import '../js/js.dart' as js show js, Template, Expression, Name;
-import '../ssa/ssa.dart' show TypeMaskFactory;
+import '../ssa/types.dart' show TypeMaskFactory;
 import '../util/util.dart';
 
 import 'package:js_runtime/shared/embedded_names.dart'
     show JsBuiltin, JsGetName;
 import '../constants/values.dart';
 import 'type_mask_system.dart' show
     TypeMaskSystem;
 
 typedef void IrBuilderCallback(Element element, ir.FunctionDefinition irNode);
 
@@ skipping 3981 matching lines @@
     _backend.jsInteropAnalysis.hasAnonymousAnnotation(element.contextClass);
 
   String getJsInteropTargetPath(FunctionElement element) {
     return '${_backend.namer.fixedBackendPath(element)}.'
       '${_backend.getFixedBackendName(element)}';
   }
 
   DartType get jsJavascriptObjectType =>
     _backend.helpers.jsJavaScriptObjectClass.thisType;
 }