Ensure that cref completion uses Speculative SemanticModel. Fixes TFS #988380

src/Features/CSharp/Completion/CompletionProviders/CrefCompletionProvider.cs

@@ -76,7 +76,11 @@ protected override async Task<IEnumerable<CompletionItem>> GetItemsWorkerAsync(D
             }
 
             var result = SpecializedCollections.EmptyEnumerable<ISymbol>();
-            var semanticModel = await document.GetCSharpSemanticModelForNodeAsync(token.Parent, cancellationToken).ConfigureAwait(false);
+
+            // To get a Speculative SemanticModel (which is much faster), we need to 
+            // walk up to the node the DocumentationTrivia is attached to.
+            var parentNode = token.GetAncestor<DocumentationCommentTriviaSyntax>().ParentTrivia.Token.Parent;
+            var semanticModel = await document.GetCSharpSemanticModelForNodeAsync(parentNode, cancellationToken).ConfigureAwait(false);
 
             // cref ""|, ""|"", ""a|""
             if (token.IsKind(SyntaxKind.DoubleQuoteToken, SyntaxKind.SingleQuoteToken) && token.Parent.IsKind(SyntaxKind.XmlCrefAttribute))

src/Features/VisualBasic/Completion/CompletionProviders/CrefCompletionProvider.vb

@@ -59,7 +59,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Completion.Providers
                 Return Nothing
             End If
 
-            Dim semanticModel = Await document.GetVisualBasicSemanticModelForNodeAsync(touchingToken.Parent, cancellationToken).ConfigureAwait(False)
+            ' To get a Speculative SemanticModel (which is much faster), we need to 
+            ' walk up to the node the DocumentationTrivia is attached to.
+            Dim parentNode = token.GetAncestor(Of DocumentationCommentTriviaSyntax)().ParentTrivia.Token.Parent
+            Dim semanticModel = Await document.GetVisualBasicSemanticModelForNodeAsync(parentNode, cancellationToken).ConfigureAwait(False)
             Dim workspace = document.Project.Solution.Workspace
 
             If IsXmlStringContext(touchingToken) OrElse