Fix LogMan tracer to work correctly when process ids are reused.

tools/isolate/trace_inputs.py

 #!/usr/bin/env python
 # coding=utf-8
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Traces an executable and its child processes and extract the files accessed
 by them.
 
 The implementation uses OS-specific API. The native Kernel logger and the ETL
@@ skipping 2438 matching lines @@
         return
       # Override any stale file object
       proc.file_objects[file_object] = filepath
 
     def handle_FileIo_Rename(self, line):
       # TODO(maruel): Handle?
       pass
 
     def handle_Process_End(self, line):
       pid = line[self.PID]
-      if pid in self._process_lookup:
+      if self._process_lookup.get(pid):
         logging.info('Terminated: %d' % pid)
         self._process_lookup[pid] = None
       else:
         logging.debug('Terminated: %d' % pid)
 
     def handle_Process_Start(self, line):
       """Handles a new child process started by PID."""
       #UNIQUE_PROCESS_KEY = self.USER_DATA
       PROCESS_ID = self.USER_DATA + 1
       #PARENT_PID = self.USER_DATA + 2
@@ skipping 14 matching lines @@
         # Need to ignore processes we don't know about because the log is
         # system-wide. self._tracer_pid shall start only one process.
         if self.root_process:
           raise TracingFailure(
               ( 'Parent process is _tracer_pid(%d) but root_process(%d) is '
                 'already set') % (self._tracer_pid, self.root_process.pid),
               None, None, None)
         proc = self.Process(self.blacklist, pid, None)
         self.root_process = proc
         ppid = None
-      elif ppid in self._process_lookup:
+      elif self._process_lookup.get(ppid):
         proc = self.Process(self.blacklist, pid, None)
         self._process_lookup[ppid].children.append(proc)
       else:
         # Ignore
         return
       self._process_lookup[pid] = proc
 
       if (not line[IMAGE_FILE_NAME].startswith('"') or
           not line[IMAGE_FILE_NAME].endswith('"')):
         raise TracingFailure(
@@ skipping 695 matching lines @@
     return command(argv[1:])
   except TracingFailure, e:
     sys.stderr.write('\nError: ')
     sys.stderr.write(str(e))
     sys.stderr.write('\n')
     return 1
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))