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

pkg/compiler/lib/src/compiler.dart

 // Copyright (c) 2012, 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.compiler_base;
 
 import 'dart:async' show
     EventSink,
     Future;
 
@@ skipping 91 matching lines @@
 import 'resolution/resolution.dart' show
     ResolverTask;
 import 'resolution/tree_elements.dart' show
     TreeElementMapping;
 import 'scanner/scanner_task.dart' show
     ScannerTask;
 import 'serialization/task.dart' show
     SerializationTask;
 import 'script.dart' show
     Script;
-import 'ssa/ssa.dart' show
+import 'ssa/nodes.dart' show
     HInstruction;
 import 'tracer.dart' show
     Tracer;
 import 'tokens/token.dart' show
     StringToken,
     Token,
     TokenPair;
 import 'tokens/token_constants.dart' as Tokens show
     COMMENT_TOKEN,
     EOF_TOKEN;
@@ skipping 2080 matching lines @@
     if (_otherDependencies == null) {
       _otherDependencies = new Setlet<Element>();
     }
     _otherDependencies.add(element.implementation);
   }
 
   Iterable<Element> get otherDependencies {
     return _otherDependencies != null ? _otherDependencies : const <Element>[];
   }
 }