Make EncodedStringText fallback encoding lazy instead of eagerly initialized in static ctor

src/Compilers/Core/CodeAnalysisTest/Text/StringTextDecodingTests.cs

@@ -44,7 +44,7 @@ private static SourceText CreateMemoryStreamBasedEncodedText(byte[] bytes, Encod
 
             using (var stream = new MemoryStream(buffer, 0, bytes.Length, writable: true, publiclyVisible: true))
             {
-                return EncodedStringText.Create(stream, getEncoding, readEncodingOpt, algorithm);
+                return EncodedStringText.Create(stream, new Lazy<Encoding>(getEncoding), readEncodingOpt, algorithm);
             }
         }
 

src/Compilers/Core/Portable/EncodedStringText.cs

@@ -24,7 +24,7 @@ internal static class EncodedStringText
         ///     2. CodePage 1252.
         ///     3. Latin1.
         /// </summary>
-        private static readonly Encoding s_fallbackEncoding = GetFallbackEncoding();
+        private static readonly Lazy<Encoding> s_fallbackEncoding = new Lazy<Encoding>(GetFallbackEncoding);
 
         private static Encoding GetFallbackEncoding()
         {
@@ -72,13 +72,13 @@ private static Encoding GetFallbackEncoding()
             SourceHashAlgorithm checksumAlgorithm = SourceHashAlgorithm.Sha1)
         {
             return Create(stream,
-                () => s_fallbackEncoding,
+                s_fallbackEncoding,
                 defaultEncoding: defaultEncoding,
                 checksumAlgorithm: checksumAlgorithm);
         }
 
         // internal for testing
-        internal static SourceText Create(Stream stream, Func<Encoding> getEncoding,
+        internal static SourceText Create(Stream stream, Lazy<Encoding> getEncoding,
             Encoding defaultEncoding = null,
             SourceHashAlgorithm checksumAlgorithm = SourceHashAlgorithm.Sha1)
         {
@@ -100,7 +100,7 @@ private static Encoding GetFallbackEncoding()
 
             try
             {
-                return Decode(stream, defaultEncoding ?? getEncoding(), checksumAlgorithm, throwIfBinaryDetected: detectEncoding);
+                return Decode(stream, defaultEncoding ?? getEncoding.Value, checksumAlgorithm, throwIfBinaryDetected: detectEncoding);
             }
             catch (DecoderFallbackException e)
             {