fix hashtags: double colons are not hashtags

Bug: 896110
Change-Id: Ibaf36df48d9ea25e8ee633ca505fa7f7c2063df4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1944639
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Anthony Polito <apolito@google.com>

git_cl.py

@@ -2830,7 +2830,7 @@ class ChangeDescription(object):
   CHERRY_PICK_LINE = r'^\(cherry picked from commit [a-fA-F0-9]{40}\)$'
   STRIP_HASH_TAG_PREFIX = r'^(\s*(revert|reland)( "|:)?\s*)*'
   BRACKET_HASH_TAG = r'\s*\[([^\[\]]+)\]'
-  COLON_SEPARATED_HASH_TAG = r'^([a-zA-Z0-9_\- ]+):'
+  COLON_SEPARATED_HASH_TAG = r'^([a-zA-Z0-9_\- ]+):($|[^:])'
   BAD_HASH_TAG_CHUNK = r'[^a-zA-Z0-9]+'
 
   def __init__(self, description, bug=None, fixed=None):

tests/git_cl_test.py

@@ -1694,6 +1694,8 @@ class TestGitCl(TestCase):
       ('Revert "Reland: [a] feature"', ['a']),
       ('Foo: feature', ['foo']),
       ('Foo Bar: feature', ['foo-bar']),
+      ('Change Foo::Bar', []),
+      ('Foo: Change Foo::Bar', ['foo']),
       ('Revert "Foo bar: feature"', ['foo-bar']),
       ('Reland "Foo bar: feature"', ['foo-bar']),
     ]