feat(chromium): roll Chromium to r615489 (#3653)

This roll includes:
- https://crrev.com/611230 - Headless: enable disk cache for default profile
- https://crrev.com/613297 - headless: support --disk-cache-dir flag

package.json

@@ -8,7 +8,7 @@
     "node": ">=6.4.0"
   },
   "puppeteer": {
-    "chromium_revision": "609904"
+    "chromium_revision": "615489"
   },
   "scripts": {
     "unit": "node test/test.js",