Fix linter error

Author: rbuckton

src/compiler/visitor.ts

@@ -587,7 +587,7 @@ namespace ts {
                 }
                 if (visited) {
                     if (isArray(visited)) {
-                        for (let visitedNode of visited) {
+                        for (const visitedNode of visited) {
                             Debug.assertNode(visitedNode, test);
                             aggregateTransformFlags(visitedNode);
                             updated.push(<T>visitedNode);

src/services/transform.ts

@@ -0,0 +1,29 @@
+/// <reference path="..\compiler\transformer.ts"/>
+/// <reference path="transpile.ts"/>
+namespace ts {
+    /**
+     * Transform one or more source files using the supplied transformers.
+     * @param source A `SourceFile` or an array of `SourceFiles`.
+     * @param transformers An array of `Transformer` callbacks used to process the transformation.
+     */
+    export function transform(source: SourceFile | SourceFile[], transformers: Transformer[]) {
+        const diagnostics: Diagnostic[] = [];
+        const compilerOptions: CompilerOptions = {};
+        const sourceFiles = isArray(source) ? source : [source];
+        const fileMap = arrayToMap(sourceFiles, sourceFile => sourceFile.fileName);
+        const emitHost: EmitHost = {
+            getCompilerOptions: () => compilerOptions,
+            getCanonicalFileName: fileName => fileName,
+            getCommonSourceDirectory: () => "",
+            getCurrentDirectory: () => "",
+            getNewLine: () => "\n",
+            getSourceFile: fileName => fileMap.get(fileName),
+            getSourceFileByPath: fileName => fileMap.get(fileName),
+            getSourceFiles: () => sourceFiles,
+            isSourceFileFromExternalLibrary: () => false,
+            isEmitBlocked: () => false,
+            writeFile: () => Debug.fail("'writeFile()' is not supported during transformation.")
+        };
+        return transformFiles(/*resolver*/ undefined, emitHost, sourceFiles, transformers);
+    }
+}