DevTools: Support ECMAScript 9 (2018) features

This change updates our eslint configuration to parse ECMAScript 9
syntax which includes the object literal spread operator.

Change-Id: I9fadc40b2832e92a32f4ee94fddaf9c719046413
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1639178Reviewed-by: Joel Einbinder <einbinder@chromium.org>
Commit-Queue: John Emau <johnemau@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#666325}

third_party/blink/renderer/devtools/.eslintrc.js

@@ -7,7 +7,7 @@ module.exports = {
     },
 
     "parserOptions": {
-        "ecmaVersion": 8
+        "ecmaVersion": 9
     },
 
     /**