[Release] Activate merge watchlist

R=machenbach@chromium.org
NOTRY=true
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/1670513002

Cr-Commit-Position: refs/branch-heads/4.8@{crosswalk-project#22}
Cr-Branched-From: 10449d4-refs/heads/4.8.271@{#1}
Cr-Branched-From: 2ebd5fc-refs/heads/master@{#31941}

WATCHLISTS

@@ -50,6 +50,9 @@
     'feature_shipping_status': {
       'filepath': 'src/flag-definitions.h',
     },
+    'merges': {
+      'filepath': '.',
+    },
   },
 
   'WATCHLISTS': {
@@ -69,5 +72,9 @@
     'feature_shipping_status': [
       'hablich@chromium.org',
     ],
+    'merges': [
+      # Only enabled on branches created with tools/release/create_release.py
+      'v8-merges@googlegroups.com',
+    ],
   },
 }