misc: Update references to Runtime.cachedResources

These references will be properly namespace-scoped once [1] is
submitted.

[1]: https://polymer2-chromium-review.googlesource.com/c/chromium/src/+/1829708

build/build-dt-report-resources.js

@@ -17,7 +17,7 @@ const generatorFilename = `./lighthouse-core/report/report-generator.js`;
 const htmlReportAssets = require('../lighthouse-core/report/html/html-report-assets.js');
 
 /**
- * Used to save cached resources (Runtime.cachedResources).
+ * Used to save cached resources (Root.Runtime.cachedResources).
  * @param {string} name
  * @param {string} content
  */

clients/devtools-report-assets.js

@@ -7,14 +7,14 @@
 
 /**
  * @fileoverview Instead of loading report assets form the filesystem, in Devtools we must load
- * them via Runtime.cachedResources. We use this module to shim
+ * them via Root.Runtime.cachedResources. We use this module to shim
  * lighthouse-core/report/html/html-report-assets.js in Devtools.
  */
 
-/* global Runtime */
+/* global Root */
 
-// @ts-ignore: Runtime exists in Devtools.
-const cachedResources = Runtime.cachedResources;
+// @ts-ignore: Root.Runtime exists in Devtools.
+const cachedResources = Root.Runtime.cachedResources;
 
 // Getters are necessary because the DevTools bundling processes
 // resources after this module is resolved. These properties are not