Tweak the pdf watchlist entry to improve matching.

Add a slash at the end of the regex entries, to only watch those
directories, so random files with "pdf" in the name do not match.

Change-Id: I75a6f8a139c85e54bd283f379bfbd169ed186691
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1669895
Reviewed-by: Tommy Li <[email protected]>
Commit-Queue: Lei Zhang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#671153}
diff --git a/WATCHLISTS b/WATCHLISTS
index 83d6aa0..2f1a0fa 100644
--- a/WATCHLISTS
+++ b/WATCHLISTS
@@ -1418,10 +1418,10 @@
                   '|ios/web/public/payments'
     },
     'pdf': {
-      'filepath': 'components/pdf'\
-                  '|chrome/browser/pdf'\
-                  '|chrome/browser/ui/pdf'\
-                  '|pdf'
+      'filepath': 'components/pdf/'\
+                  '|chrome/browser/pdf/'\
+                  '|chrome/browser/ui/pdf/'\
+                  '|pdf/'
     },
     'pepper_api': {
       'filepath': 'ppapi/api'\