def _CheckForUseOfWrongClock(input_api, output_api):
  """Make sure new lines of media code don't use a clock susceptible to skew."""

  def FilterFile(affected_file):
    """Return true if the file could contain code referencing base::Time."""
    return affected_file.LocalPath().endswith(
        ('.h', '.cc', '.cpp', '.cxx', '.mm'))

  # Regular expression that should detect any explicit references to the
  # base::Time type (or base::Clock/DefaultClock), whether in using decls,
  # typedefs, or to call static methods.
  base_time_type_pattern = r'(^|\W)base::(Time|Clock|DefaultClock)(\W|$)'

  # Regular expression that should detect references to the base::Time class
  # members, such as a call to base::Time::Now.
  base_time_member_pattern = r'(^|\W)(Time|Clock|DefaultClock)::'

  # Regular expression to detect "using base::Time" declarations.  We want to
  # prevent these from triggerring a warning.  For example, it's perfectly
  # reasonable for code to be written like this:
  #
  #   using base::Time;
  #   ...
  #   int64 foo_us = foo_s * Time::kMicrosecondsPerSecond;
  using_base_time_decl_pattern = r'^\s*using\s+(::)?base::Time\s*;'

  # Regular expression to detect references to the kXXX constants in the
  # base::Time class.  We want to prevent these from triggerring a warning.
  base_time_konstant_pattern = r'(^|\W)Time::k\w+'

  problem_re = input_api.re.compile(
      r'(' + base_time_type_pattern + r')|(' + base_time_member_pattern + r')')
  exception_re = input_api.re.compile(
      r'(' + using_base_time_decl_pattern + r')|(' +
      base_time_konstant_pattern + r')')
  problems = []
  for f in input_api.AffectedSourceFiles(FilterFile):
    for line_number, line in f.ChangedContents():
      if problem_re.search(line):
        if not exception_re.search(line):
          problems.append(
              '  %s:%d\n    %s' % (f.LocalPath(), line_number, line.strip()))

  if problems:
    return [output_api.PresubmitPromptOrNotify(
        'You added one or more references to the base::Time class and/or one\n'
        'of its member functions (or base::Clock/DefaultClock). In media\n'
        'code, it is rarely correct to use a clock susceptible to time skew!\n'
        'Instead, could you use base::TimeTicks to track the passage of\n'
        'real-world time?\n\n' +
        '\n'.join(problems))]
  else:
    return []