Ensure the runtime is appended to output bundles.

Needed for ES6 modules in bundles.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=186339854

src/com/google/javascript/jscomp/AbstractCommandLineRunner.java

@@ -264,6 +264,11 @@ protected CommandLineConfig getCommandLineConfig() {
   protected abstract void prepForBundleAndAppendTo(
       Appendable out, CompilerInput input, String content) throws IOException;
 
+  /**
+   * Writes whatever runtime libraries are needed to bundle.
+   */
+  protected abstract void appendRuntimeTo(Appendable out) throws IOException;
+
   /**
    * Returns the instance of the Options to use when {@link #run()} is called. createCompiler() is
    * called before createOptions(), so getCompiler() will not return null when createOptions() is
@@ -2034,6 +2039,16 @@ void printManifestTo(Iterable<CompilerInput> inputs, Appendable out)
   @VisibleForTesting
   void printBundleTo(Iterable<CompilerInput> inputs, Appendable out)
       throws IOException {
+    if (!compiler.getOptions().preventLibraryInjection) {
+      // ES6 modules will need a runtime in a bundle. Skip appending this runtime if there are no
+      // ES6 modules to cut down on size.
+      for (CompilerInput input : inputs) {
+        if ("es6".equals(input.getLoadFlags().get("module"))) {
+          appendRuntimeTo(out);
+          break;
+        }
+      }
+    }
 
     for (CompilerInput input : inputs) {
       // Every module has an empty file in it. This makes it easier to implement

src/com/google/javascript/jscomp/CommandLineRunner.java

@@ -1834,7 +1834,13 @@ protected Compiler createCompiler() {
   @Override
   protected void prepForBundleAndAppendTo(Appendable out, CompilerInput input, String content)
       throws IOException {
-    ClosureBundler.appendInput(out, input, content);
+    new ClosureBundler().withPath(input.getName()).appendInput(out, input, content);
+  }
+
+  @Override
+  protected void appendRuntimeTo(Appendable out)
+      throws IOException {
+    new ClosureBundler().appendRuntimeTo(out);
   }
 
   @Override