Rename TranslateUri to UriTranslator, rename files, extract Impl.

pkg/front_end/lib/src/dependency_grapher_impl.dart

Index: pkg/front_end/lib/src/dependency_grapher_impl.dart
diff --git a/pkg/front_end/lib/src/dependency_grapher_impl.dart b/pkg/front_end/lib/src/dependency_grapher_impl.dart
index a4bd5b7ba36610451b844e8411cc6f087e6f40f8..a4d285313821e3915246985fe0941d723e8b0960 100644
--- a/pkg/front_end/lib/src/dependency_grapher_impl.dart
+++ b/pkg/front_end/lib/src/dependency_grapher_impl.dart
@@ -10,7 +10,7 @@ import 'package:front_end/src/base/processed_options.dart';
 import 'package:front_end/src/fasta/parser.dart';
 import 'package:front_end/src/fasta/scanner.dart';
 import 'package:front_end/src/fasta/source/directive_listener.dart';
-import 'package:front_end/src/fasta/translate_uri.dart';
+import 'package:front_end/src/fasta/uri_translator.dart';
 
 /// Generates a representation of the dependency graph of a program.
 ///
@@ -25,7 +25,7 @@ import 'package:front_end/src/fasta/translate_uri.dart';
 /// package:front_end/dependency_grapher.dart.
 Future<Graph> graphForProgram(List<Uri> sources, ProcessedOptions options,
     {FileReader fileReader}) async {
-  TranslateUri uriTranslator = await options.getUriTranslator();
+  UriTranslator uriTranslator = await options.getUriTranslator();
   fileReader ??= (originalUri, resolvedUri) =>
       options.fileSystem.entityForUri(resolvedUri).readAsString();
   var walker = new _Walker(fileReader, uriTranslator, options.compileSdk);
@@ -50,7 +50,7 @@ class _StartingPoint extends _WalkerNode {
 
 class _Walker extends AsyncDependencyWalker<_WalkerNode> {
   final FileReader fileReader;
-  final TranslateUri uriTranslator;
+  final UriTranslator uriTranslator;
   final _nodesByUri = <Uri, _WalkerNode>{};
   final graph = new Graph();
   final bool compileSdk;