Share more code, and prevent an allocation when input is null.

src/Compilers/CSharp/Portable/Syntax/SyntaxFactory.cs

@@ -1365,11 +1365,7 @@ public static SyntaxTriviaList TriviaList(params SyntaxTrivia[] trivias)
         /// </summary>
         /// <param name="trivias">A sequence of trivia.</param>
         public static SyntaxTriviaList TriviaList(IEnumerable<SyntaxTrivia> trivias)
-        {
-            var builder = SyntaxTriviaListBuilder.Create();
-            builder.AddRange(trivias);
-            return builder.ToList();
-        }
+            => SyntaxTriviaListBuilder.Create(trivias);
 
         /// <summary>
         /// Creates an empty separated list.

src/Compilers/Core/Portable/Syntax/SyntaxTriviaListBuilder.cs

@@ -21,6 +21,18 @@ public static SyntaxTriviaListBuilder Create()
             return new SyntaxTriviaListBuilder(4);
         }
 
+        public static SyntaxTriviaList Create(IEnumerable<SyntaxTrivia> trivia)
+        {
+            if (trivia == null)
+            {
+                return new SyntaxTriviaList();
+            }
+
+            var builder = SyntaxTriviaListBuilder.Create();
+            builder.AddRange(trivia);
+            return builder.ToList();
+        }
+
         public int Count
         {
             get { return _count; }

src/Compilers/VisualBasic/Portable/Syntax/SyntaxNodeFactories.vb

@@ -825,9 +825,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         ''' </summary>
         ''' <param name="trivias">A sequence of trivia.</param>
         Public Shared Function TriviaList(trivias As IEnumerable(Of SyntaxTrivia)) As SyntaxTriviaList
-            Dim builder = SyntaxTriviaListBuilder.Create()
-            builder.AddRange(trivias)
-            Return builder.ToList()
+            Return SyntaxTriviaListBuilder.Create(trivias)
         End Function
 
         ''' <summary>