Add RandomString() and its test, and use it everywhere it makes sense

util/net/http_transport_test_server.py

 #!/usr/bin/env python
 # coding: utf-8
 
 # Copyright 2014 The Crashpad Authors. All rights reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #     http://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
 """A one-shot testing webserver.
 
 When invoked, this server will write a short integer to stdout, indiciating on
 which port the server is listening. It will then read one integer from stdin,
 indiciating the response code to be sent in response to a request. It also reads
-8 characters from stdin, which, after having "\r\n" appended, will form the
+16 characters from stdin, which, after having "\r\n" appended, will form the
 response body in a successful response (one with code 200). The server will
 process one HTTP request, deliver the prearranged response to the client, and
 write the entire request to stdout. It will then terminate.
 
 This server is written in Python since it provides a simple HTTP stack, and
 because parsing Chunked encoding is safer and easier in a memory-safe language.
 This could easily have been written in C++ instead.
 """
 
 import BaseHTTPServer
@@ skipping 103 matching lines @@
     msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
 
   # Start the server.
   server = BaseHTTPServer.HTTPServer(('127.0.0.1', 0), RequestHandler)
 
   # Write the port as an unsigned short to the parent process.
   sys.stdout.write(struct.pack('=H', server.server_address[1]))
   sys.stdout.flush()
 
   # Read the desired test response code as an unsigned short and the desired
-  # response body as an 8-byte string from the parent process.
+  # response body as a 16-byte string from the parent process.
   RequestHandler.response_code, RequestHandler.response_body = \
-      struct.unpack('=H8s', sys.stdin.read(struct.calcsize('=H8s')))
+      struct.unpack('=H16s', sys.stdin.read(struct.calcsize('=H16s')))
 
   # Handle the request.
   server.handle_request()
 
   # Share the entire request with the test program, which will validate it.
   sys.stdout.write(RequestHandler.raw_request)
   sys.stdout.flush()
 
 if __name__ == '__main__':
   Main()