Don't allocate a lambda each time we get a hashcode for a named type.

src/Workspaces/Core/Portable/Shared/Utilities/SymbolEquivalenceComparer.GetHashCodeVisitor.cs

@@ -19,6 +19,7 @@ private class GetHashCodeVisitor
             private readonly bool _objectAndDynamicCompareEqually;
             private readonly Func<int, IParameterSymbol, int> _parameterAggregator;
             private readonly Func<int, ISymbol, int> _symbolAggregator;
+            private readonly Func<int, INamedTypeSymbol, int> _namedTypeAggregator;
 
             public GetHashCodeVisitor(
                 SymbolEquivalenceComparer symbolEquivalenceComparer,
@@ -30,6 +31,7 @@ private class GetHashCodeVisitor
                 _objectAndDynamicCompareEqually = objectAndDynamicCompareEqually;
                 _parameterAggregator = (acc, sym) => Hash.Combine(symbolEquivalenceComparer.ParameterEquivalenceComparer.GetHashCode(sym), acc);
                 _symbolAggregator = (acc, sym) => GetHashCode(sym, acc);
+                _namedTypeAggregator = CombineNamedTypeHashCode;
             }
 
             public int GetHashCode(ISymbol x, int currentHash)
@@ -169,10 +171,10 @@ private int CombineHashCodes(IModuleSymbol x, int currentHash)
 
             private int CombineHashCodes(INamedTypeSymbol x, int currentHash)
             {
-                return Unwrap(x).Aggregate(currentHash, (a, n) => CombineNamedTypeHashCode(n, a));
+                return Unwrap(x).Aggregate(currentHash, _namedTypeAggregator);
             }
 
-            private int CombineNamedTypeHashCode(INamedTypeSymbol x, int currentHash)
+            private int CombineNamedTypeHashCode(int currentHash, INamedTypeSymbol x)
             {
                 // If we want object and dynamic to be the same, and this is 'object', then return
                 // the same hash we do for 'dynamic'.