Add a JSON logging handler to the Kasko integration tests.

chrome/test/kasko/py/kasko/json_logging_handler.py

Index: chrome/test/kasko/py/kasko/json_logging_handler.py
diff --git a/chrome/test/kasko/py/kasko/json_logging_handler.py b/chrome/test/kasko/py/kasko/json_logging_handler.py
new file mode 100755
index 0000000000000000000000000000000000000000..8a26c38bc96f5501ebdf24b18788c57fc48a3d81
--- /dev/null
+++ b/chrome/test/kasko/py/kasko/json_logging_handler.py
@@ -0,0 +1,30 @@
+#!/usr/bin/env python
+# Copyright 2016 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.
+
+"""Logging handler used to log into a JSON file."""
+
+import json
+import logging
+
+
+class JSONLoggingHandler(logging.Handler):
+  """A logging handler that forwards log messages into a JSON file."""
+
+  def __init__(self, json_file):
+    logging.Handler.__init__(self)
+    formatter = logging.Formatter('%(name)s:%(message)s')
+    self.setFormatter(formatter)
+    self.json_file_ = json_file
+    self.log_messages_ = []
+
+  def close(self):
+    """Dump the list of log messages into the JSON file."""
+    with open(self.json_file_, 'w') as f:
+      f.write(json.dumps(self.log_messages_))
+    logging.Handler.close(self)
+
+  def emit(self, record):
+    """Append the record to list of messages."""
+    self.log_messages_.append({record.levelname: self.format(record)})