Support a tag to ignore long lines

Long lines in source files are bad, but sometimes unavoidable. Since
ignoring warnings is even worse than long lines it is wise to have a way
to disable the warning. This change adds support for a multi-language
tag that can be put in unavoidably long lines.

Bug: 1309977
Change-Id: I205086050b5aa5b4a02a651c06615c82ec0e1a38
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3896084
Reviewed-by: Dmitrii Kuragin <kuragin@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>

presubmit_canned_checks.py

@@ -529,6 +529,7 @@ def CheckLongLines(input_api, output_api, maxlen, source_file_filter=None):
   ]
 
   def no_long_lines(file_extension, line):
+    """Returns True if the line length is okay."""
     # Check for language specific exceptions.
     if any(file_extension in exts and line.lstrip().startswith(exceptions)
            for exts, exceptions in LANGUAGE_EXCEPTIONS):
@@ -548,6 +549,9 @@ def CheckLongLines(input_api, output_api, maxlen, source_file_filter=None):
     if any((url in line) for url in ('file://', 'http://', 'https://')):
       return True
 
+    if 'presubmit: ignore-long-line' in line:
+      return True
+
     if line_len > extra_maxlen:
       return False