Bugfix 1094427. Fix flaky Testcase.

Call WithDocumentText when fed with the same text sometimes doesn't return the same instance of the Document because TextSource, a WeakReference, sometimes loses the reference and the perf optimization to return the same instance of the Document is not possbile. (changeset 1387876)

Src/Workspaces/Core/Portable/CodeCleanup/Providers/FormatCodeCleanupProvider.cs

@@ -22,7 +22,13 @@ public async Task<Document> CleanupAsync(Document document, IEnumerable<TextSpan
             if (document.TryGetText(out oldText))
             {
                 var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
-                var newText = oldText.WithChanges(Formatter.GetFormattedTextChanges(root, spans, document.Project.Solution.Workspace, cancellationToken: cancellationToken));
+                var textChanges = Formatter.GetFormattedTextChanges(root, spans, document.Project.Solution.Workspace, cancellationToken: cancellationToken);
+                if (textChanges.Count == 0)
+                {
+                    return document;
+                }
+
+                var newText = oldText.WithChanges(textChanges);
                 return document.WithText(newText);
             }