Domain Reliability: Update mail.google.com config.

Just a small update to the baked-in config for mail.google.com.

BUG=

Review URL: https://codereview.chromium.org/945443002

Cr-Commit-Position: refs/heads/master@{#317100}

components/domain_reliability/baked_in_configs/mail_google_com.json

 {
-  "config_version": "mail-google-com $Revision: #5 $",
+  "config_version": "mail-google-com $Revision: #6 $",
   "config_valid_until": 1446336000,
   "monitored_domain": "mail.google.com",
   "collectors": [
@@ -26,6 +26,12 @@
       "success_sample_rate": 0.05,
       "failure_sample_rate": 1.00
     },
+    {
+      "resource_name": "gmail-persistent",
+      "url_patterns": ["http*://mail.google.com/*/channel/bind*"],
+      "success_sample_rate": 0.05,
+      "failure_sample_rate": 1.00
+    },
     {
       "resource_name": "gmail-other",
       "url_patterns": ["*"],