Don't use a name that we then have to undo.

src/Workspaces/CSharp/Portable/LanguageServices/CSharpSyntaxFactsService.cs

@@ -844,7 +844,7 @@ public bool TryGetDeclaredSymbolInfo(SyntaxNode node, out DeclaredSymbolInfo dec
                 case SyntaxKind.IndexerDeclaration:
                     var indexerDecl = (IndexerDeclarationSyntax)node;
                     declaredSymbolInfo = new DeclaredSymbolInfo(
-                        WellKnownMemberNames.Indexer, GetIndexerSuffix(indexerDecl),
+                        "this", GetIndexerSuffix(indexerDecl),
                         GetContainerDisplayName(node.Parent),
                         GetFullyQualifiedContainerName(node.Parent),
                         DeclaredSymbolInfoKind.Indexer,

src/Workspaces/Core/Portable/FindSymbols/SyntaxTree/SyntaxTreeIndex_Persistence.cs

@@ -15,7 +15,7 @@ namespace Microsoft.CodeAnalysis.FindSymbols
     internal sealed partial class SyntaxTreeIndex : IObjectWritable
     {
         private const string PersistenceName = "<TreeInfoPersistence>";
-        private const string SerializationFormat = "4";
+        private const string SerializationFormat = "5";
 
         /// <summary>
         /// in memory cache will hold onto any info related to opened documents in primary branch or all documents in forked branch