[omnibox] Update watchlist to include WebUI directory.

Additionally, update the other patterns to only match at the beginning
to avoid inadvertently picking up similarly named directories under
other paths (currently just ios/chrome/browser/ui/omnibox).

Change-Id: I6da957f06af0de4b13c344cbbcdfae65a7e74821
Reviewed-on: https://chromium-review.googlesource.com/c/1327554Reviewed-by: Kevin Bailey <krb@chromium.org>
Commit-Queue: Justin Donnelly <jdonnelly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606669}

WATCHLISTS

@@ -1297,12 +1297,13 @@
                   '|chrome/android/java/src/org/chromium/chrome/browser/offlinepages/'
     },
     'omnibox': {
-      'filepath': 'chrome/browser/autocomplete/|'\
-                  'chrome/browser/ui/location_bar/|'\
-                  'chrome/browser/ui/omnibox/|'\
-                  'chrome/browser/ui/.*/location_bar/|'\
-                  'chrome/browser/ui/.*/omnibox/|'\
-                  'components/omnibox/'
+      'filepath': '^chrome/browser/autocomplete/|'\
+                  '^chrome/browser/resources/omnibox|'\
+                  '^chrome/browser/ui/location_bar/|'\
+                  '^chrome/browser/ui/omnibox/|'\
+                  '^chrome/browser/ui/.*/location_bar/|'\
+                  '^chrome/browser/ui/.*/omnibox/|'\
+                  '^components/omnibox/'
     },
     'optimization_guide': {
       'filepath': 'optimization_guide|'\