Support browser caching using hashes in serverMode (fixes #93, fixes #92)

lib/src/codegen/dart_codegen.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.
 
 library dev_compiler.src.codegen.dart_codegen;
 
 import 'dart:io' show File;
 
 import 'package:analyzer/analyzer.dart' as analyzer;
 import 'package:analyzer/src/generated/ast.dart';
@@ skipping 434 matching lines @@
     }
     isLib(unit) => unit.directives.any((d) => d is LibraryDirective);
     isNotLib(unit) => !isLib(unit);
     var libs = units.where(isLib);
     var parts = units.where(isNotLib);
     assert(libs.length == 1 || (libs.length == 0 && parts.length == 1));
     parts.forEach(doOne);
     libs.forEach(doOne);
   }
 
-  void generateLibrary(Iterable<CompilationUnit> units, LibraryInfo info,
+  String generateLibrary(Iterable<CompilationUnit> units, LibraryInfo info,
       CheckerReporter reporter) {
     _vm = new reifier.VariableManager();
     _extraImports = new Set<LibraryElement>();
     _generateLibrary(units, info, reporter);
     _extraImports = null;
     _vm = null;
+    return null;
   }
 }
 
 class EmptyUnitGenerator extends UnitGeneratorCommon {
   final java_core.PrintWriter _out;
   CompilationUnit unit;
 
   EmptyUnitGenerator(this.unit, java_core.PrintWriter out)
       : _out = out,
         super(out);
 
   void output(String s) => _out.print(s);
   void outputln(String s) => _out.println(s);
 
   void generate() {
     unit.visitChildren(this);
   }
 }
 
 // This class emits the code unchanged, for comparison purposes.
 class EmptyDartGenerator extends codegenerator.CodeGenerator {
   final CompilerOptions options;
 
   EmptyDartGenerator(String outDir, Uri root, TypeRules rules, this.options)
       : super(outDir, root, rules);
 
-  void generateLibrary(Iterable<CompilationUnit> units, LibraryInfo info,
+  String generateLibrary(Iterable<CompilationUnit> units, LibraryInfo info,
       CheckerReporter reporter) {
     for (var unit in units) {
       var outputDir = makeOutputDirectory(info, unit);
       reporter.enterSource(unit.element.source);
       generateUnit(unit, info, outputDir);
       reporter.leaveSource();
     }
+    return null;
   }
 
   void generateUnit(CompilationUnit unit, LibraryInfo info, String libraryDir) {
     var uri = unit.element.source.uri;
     _log.fine("Emitting original unit " + uri.toString());
     FileWriter out = new FileWriter(
         options, path.join(libraryDir, '${uri.pathSegments.last}'));
     var unitGen = new EmptyUnitGenerator(unit, out);
     unitGen.generate();
     out.finalize();
   }
 }