Create a public API for contributing fixes and make fixes pluggable

pkg/analysis_server/lib/edit/fix/fix_dart.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 analysis_server.edit.fix.fix_dart;
+
+import 'package:analysis_server/edit/fix/fix_core.dart';
+import 'package:analyzer/src/generated/ast.dart';
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/error.dart';
+import 'package:analyzer/src/generated/source.dart';
+
+/**
+ * A [FixContributor] that can be used to contribute fixes for errors in Dart
+ * files.
+ */
+abstract class DartFixContributor extends FixContributor {
+  @override
+  List<Fix> computeFixes(AnalysisContext context, AnalysisError error) {
+    Source source = error.source;
+    if (!AnalysisEngine.isDartFileName(source.fullName)) {
+      return Fix.EMPTY_LIST;
+    }
+    List<Source> libraries = context.getLibrariesContaining(source);
+    if (libraries.isEmpty) {
+      return Fix.EMPTY_LIST;
+    }
+    CompilationUnit unit =
+        context.resolveCompilationUnit2(source, libraries[0]);
+    if (unit == null) {
+      return Fix.EMPTY_LIST;
+    }
+    return internalComputeFixes(unit, error);
+  }
+
+  /**
+   * Return a list of fixes for the given [error]. The error was reported
+   * against the given compilation [unit].
+   */
+  List<Fix> internalComputeFixes(CompilationUnit unit, AnalysisError error);
+}