Use quotes that Emacs can deal with.

dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 2922 matching lines @@
       buffer.write(
           jsAst.prettyPrint(generateDispatchPropertyInitialization(),
                             compiler));
       buffer.write(N);
     }
     addComment('BEGIN invoke [main].', buffer);
     // This code finds the currently executing script by listening to the
     // onload event of all script tags and getting the first script which
     // finishes. Since onload is called immediately after execution this should
     // not substantially change execution order.
-    buffer.write("""
+    buffer.write('''
 ;(function (callback) {
-  if (typeof document === 'undefined') {
+  if (typeof document === "undefined") {
     callback(null);
     return;
   }
   if (document.currentScript) {
     callback(document.currentScript);
     return;
   }
 
   var scripts = document.scripts;
   function onLoad(event) {
     for (var i = 0; i < scripts.length; ++i) {
-      scripts[i].removeEventListener('load', onLoad, false);
+      scripts[i].removeEventListener("load", onLoad, false);
     }
     callback(event.target);
   }
   for (var i = 0; i < scripts.length; ++i) {
-    scripts[i].addEventListener('load', onLoad, false);
+    scripts[i].addEventListener("load", onLoad, false);
   }
 })(function(currentScript) {
   ${namer.isolateName}.${namer.isolatePropertiesName}.\$currentScript =
       currentScript;
 
-  if (typeof console !== 'undefined' && typeof document !== 'undefined' &&
+  if (typeof console !== "undefined" && typeof document !== "undefined" &&
       document.readyState == "loading") {
     console.warn("Dart script executed synchronously, use <script src='" +
         currentScript.src + "' defer></scr" + "ipt> to execute after parsing " +
         "has completed. See also http://dartbug.com/12281.");
   }
   if (typeof dartMainRunner === "function") {
     dartMainRunner(function() { ${mainCall}; });
   } else {
     ${mainCall};
   }
-})$N""");
+})$N''');
     addComment('END invoke [main].', buffer);
   }
 
   void emitGetInterceptorMethod(CodeBuffer buffer,
                                 String key,
                                 Set<ClassElement> classes) {
     jsAst.Statement buildReturnInterceptor(ClassElement cls) {
       return js.return_(js(namer.isolateAccess(cls))['prototype']);
     }
 
@@ skipping 1123 matching lines @@
 
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;