Add assist to convert part-of directives

pkg/analysis_server/lib/src/services/correction/assist_internal.dart

Index: pkg/analysis_server/lib/src/services/correction/assist_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
index 8328e32ae3de52e1df2f8cd09ec7ed1635f5d44e..872663bacd44cd54c212f50d0d5720f60568bcb7 100644
--- a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
@@ -128,6 +128,7 @@ class AssistProcessor {
     await _addProposal_convertToBlockFunctionBody();
     await _addProposal_convertToExpressionFunctionBody();
     await _addProposal_convertFlutterChild();
+    await _addProposal_convertPartOfToUri();
     await _addProposal_convertToForIndexLoop();
     await _addProposal_convertToIsNot_onIs();
     await _addProposal_convertToIsNot_onNot();
@@ -655,6 +656,23 @@ class AssistProcessor {
     _addAssistFromBuilder(changeBuilder, DartAssistKind.CONVERT_INTO_GETTER);
   }
 
+  Future<Null> _addProposal_convertPartOfToUri() async {
+    PartOfDirective directive =
+        node.getAncestor((node) => node is PartOfDirective);
+    if (directive == null || directive.libraryName == null) {
+      return;
+    }
+    String libraryPath = unitLibraryElement.source.fullName;
+    String partPath = unit.element.source.fullName;
+    String relativePath = relative(libraryPath, from: dirname(partPath));
+    SourceRange replacementRange = range.node(directive.libraryName);
+    DartChangeBuilder changeBuilder = new DartChangeBuilder(session);
+    await changeBuilder.addFileEdit(file, (DartFileEditBuilder builder) {
+      builder.addSimpleReplacement(replacementRange, "'$relativePath'");
+    });
+    _addAssistFromBuilder(changeBuilder, DartAssistKind.CONVERT_PART_OF_TO_URI);
+  }
+
   Future<Null> _addProposal_convertToBlockFunctionBody() async {
     FunctionBody body = getEnclosingFunctionBody();
     // prepare expression body