Convert isolate.py to exclusively use .isolate files.

tools/isolate/isolate_test.py

+#!/usr/bin/env python
+# 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.
+
+import unittest
+
+import isolate
+
+
+class Isolate(unittest.TestCase):
+  def test_load_empty(self):
+    content = "{}"
+    variables = {}
+    command, infiles, read_only = isolate.load_isolate(
+        content, variables, self.fail)
+    self.assertEquals([], command)
+    self.assertEquals([], infiles)
+    self.assertEquals(None, read_only)
+
+
+if __name__ == '__main__':
+  unittest.main()