git cl split: recognize bug patterns of the form "Bug: chromium:123"

Currently, only the "Bug: 123" form is recognized.

Bug: none
Change-Id: I4348779bb14f4c02bb8781ce4fe2bd55892e8cfa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4289407
Commit-Queue: Thiago Perrotta <tperrotta@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>

split_cl.py

@@ -248,8 +248,10 @@ def SplitCl(description_file, comment_file, changelist, cmd_upload, dry_run,
       if answer.lower() != 'y':
         return 0
 
-    # Verify that the description contains a bug link.
-    bug_pattern = re.compile(r"^Bug:\s*[0-9]+", re.MULTILINE)
+    # Verify that the description contains a bug link. Examples:
+    #   Bug: 123
+    #   Bug: chromium:456
+    bug_pattern = re.compile(r"^Bug:\s*(?:[a-zA-Z]+:)?[0-9]+", re.MULTILINE)
     matches = re.findall(bug_pattern, description)
     answer = 'y'
     if not matches: