Add some doc to breakpad.py and add support for NO_BREAKPAD environment variable.

breakpad.py

 # Copyright (c) 2009 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.
 
 """Breakpad for Python.
 
-Sends a notification when a process stops on an exception."""
+Sends a notification when a process stops on an exception.
+
+It is only enabled when all these conditions are met:
+  1. hostname finishes with '.google.com'
+  2. main module name doesn't contain the word 'test'
+  3. no NO_BREAKPAD environment variable is defined
+"""
 
 import atexit
 import getpass
+import os
 import urllib
 import traceback
 import socket
 import sys
 
 
 # Configure these values.
 DEFAULT_URL = 'https://chromium-status.appspot.com/breakpad'
 
 _REGISTERED = False
 
 
 def SendStack(last_tb, stack, url=None):
   """Sends the stack trace to the breakpad server."""
   if not url:
     url = DEFAULT_URL
   print 'Sending crash report ...'
   try:
     params = {
         'args': sys.argv,
         'stack': stack,
         'user': getpass.getuser(),
         'exception': last_tb,
         'host': socket.getfqdn(),
     }
+    try:
+      # That may not always work.
+      params['exception'] = str(last_tb)
+    except:
+      pass
     request = urllib.urlopen(url, urllib.urlencode(params))
     print request.read()
     request.close()
   except IOError:
     print('There was a failure while trying to send the stack trace. Too bad.')
 
 
 def CheckForException():
   """Runs at exit. Look if there was an exception active."""
   last_value = getattr(sys, 'last_value', None)
   if last_value and not isinstance(last_value, KeyboardInterrupt):
     last_tb = getattr(sys, 'last_traceback', None)
     if last_tb:
       SendStack(repr(last_value), ''.join(traceback.format_tb(last_tb)))
 
 
 def Register():
   """Registers the callback at exit. Calling it multiple times is no-op."""
   global _REGISTERED
   if _REGISTERED:
     return
   _REGISTERED = True
   atexit.register(CheckForException)
 
 
 # Skip unit tests and we don't want anything from non-googler.
 if (not 'test' in sys.modules['__main__'].__file__ and
-    socket.getfqdn().endswith('.google.com')):
+    socket.getfqdn().endswith('.google.com') and
+    not 'NO_BREAKPAD' in os.environ):
   Register()
 
 # Uncomment this line if you want to test it out.
 #Register()