Slowly transition to the "with api.get_tracer() as tracer:".

tools/isolate/isolate.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.
 
 """Does one of the following depending on the --mode argument:
   check     Verifies all the inputs exist, touches the file specified with
             --result and exits.
   hashtable Puts a manifest file and hard links each of the inputs into the
             output directory.
@@ skipping 567 matching lines @@
       # 'C:\' and state.root_dir on another one like 'D:\'.
       product_dir = None
   if not state.result.command:
     print 'No command to run'
     return 1
   api = trace_inputs.get_api()
   logfile = state.result_file + '.log'
   try:
     result = 0
     if not os.path.isfile(logfile):
-      result, _ = api.get_tracer().trace(
-          state.result.command,
-          os.path.join(state.root_dir, state.result.relative_cwd),
-          logfile,
-          True)
+      with api.get_tracer(logfile) as tracer:
+        result, _ = tracer.trace(
+            state.result.command,
+            os.path.join(state.root_dir, state.result.relative_cwd),
+            'default',
+            True)
 
     results = trace_inputs.load_trace(logfile, state.root_dir, api)
     simplified = trace_inputs.extract_directories(state.root_dir, results.files)
     variables = isolate_common.generate_dict(
             (f.path for f in simplified),
             state.result.relative_cwd,
             product_dir)
     # Outputs in a way that is easy to merge with merge_isolate.py.
     value = {
       'conditions': [
@@ skipping 162 matching lines @@
       result_file,
       input_file,
       options.mode,
       variables,
       out_dir,
       parser.error)
 
 
 if __name__ == '__main__':
   sys.exit(main())