watchlists: add 'vaapi' entry and link it to vaapi-reviews@

TBR=marcheu@chromium.org

Change-Id: Ia318d67edc7417c687aeaf8da0f6979aa47ddcff
Reviewed-on: https://chromium-review.googlesource.com/818785
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523038}

WATCHLISTS

@@ -1502,6 +1502,9 @@
     'usb': {
       'filepath': '/usb/',
     },
+    'vaapi': {
+      'filepath': 'media/gpu/vaapi',
+    },
     'valgrind': {
       'filepath': 'valgrind',
     },
@@ -2278,6 +2281,7 @@
     'usb': ['cco3+watch@chromium.org',
             'mattreynolds+watch@chromium.org',
             'scheib+watch@chromium.org'],
+    'vaapi': ['vaapi-reviews@chromium.org'],
     'valgrind': ['bruening+watch@chromium.org',
                  'glider+watch@chromium.org'],
     'version_assembly': ['caitkp+watch@chromium.org',