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

pkg/compiler/lib/src/info/send_info.dart

 // Copyright (c) 2015, 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.
 
 /// Computes measurements about sends in a function.
 library compiler.src.info.send_info;
 
-import 'dart:convert';
-
 import 'package:dart2js_info/src/measurements.dart';
 import 'package:dart2js_info/src/util.dart' show
     recursiveDiagnosticString;
 
 import '../common.dart';
-import '../common/tasks.dart' show
-    CompilerTask;
 import '../compiler.dart' show
     Compiler;
 import '../dart_types.dart';
 import '../closure.dart';
 import '../elements/elements.dart';
 import '../elements/visitor.dart' show
     ElementVisitor;
 import '../resolution/operators.dart';
 import '../resolution/semantic_visitor.dart';
 import '../resolution/tree_elements.dart';
@@ skipping 2357 matching lines @@
   @override
   R visitClosureFieldElement(ClosureFieldElement e, A arg) {
     return visitVariableElement(e, arg);
   }
 }
 
 // TODO(sigmund): get rid of debug messages.
 _debug(String message) {
   print('debug: $message');
 }