The LexerCache short circuits the lookup of keywords whenever the text is...

 The LexerCache short circuits the lookup of keywords whenever the text is greater than the maximum keyword length.  This was being expressed as a hard coded value instead of a named constant.  Changed it to be a named constant and added a test to make sure it is up to date with the actual max keyword length (changeset 1333104)

Src/Compilers/CSharp/Portable/Parser/LexerCache.cs

@@ -30,6 +30,7 @@ internal partial class LexerCache
         private readonly TextKeyedCache<SyntaxTrivia> triviaMap;
         private readonly TextKeyedCache<SyntaxToken> tokenMap;
         private readonly CachingIdentityFactory<string, SyntaxKind> keywordKindMap;
+        internal const int MaxKeywordLength = 10;
 
         internal LexerCache()
         {
@@ -47,7 +48,7 @@ internal void Free()
 
         internal bool TryGetKeywordKind(string key, out SyntaxKind kind)
         {
-            if (key.Length > 10)
+            if (key.Length > MaxKeywordLength)
             {
                 kind = SyntaxKind.None;
                 return false;

Src/Compilers/CSharp/Test/Syntax/LexicalAndXml/LexicalTests.cs

@@ -2629,6 +2629,17 @@ public void MoreDecimalLiterals()
             AssertGoodDecimalLiteral("7922816251426433759354395033549999E-5M", "ffffffffffffffffffffffff00000000");
         }
 
+        [Fact]
+        public void TestMaxKeywordLength()
+        {
+            int max = SyntaxFacts
+                .GetKeywordKinds()
+                .Concat(SyntaxFacts.GetContextualKeywordKinds())
+                .Select(SyntaxFacts.GetText)
+                .Max(x => x.Length);
+            Assert.Equal(LexerCache.MaxKeywordLength, max);
+        }
+
         [WorkItem(545781, "DevDiv")]
         [Fact]
         public void DecimalLiteralsOtherCulture()