Add an environment variable that will cause md5_check.py to write .stamp file that is debuggable

build/android/gyp/util/md5_check.py

 # Copyright 2013 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 hashlib
 import os
 
 
+# When set, record_path will include a per-file breakdown of md5s so that it is
+# possible to see exactly which file changed.
+_RECORD_EXTRA_INFO = int(os.environ.get('RECORD_EXTRA_MD5_INFO', 0))
+
+
 def CallAndRecordIfStale(
     function, record_path=None, input_paths=None, input_strings=None,
     force=False):
   """Calls function if the md5sum of the input paths/strings has changed.
 
   The md5sum of the inputs is compared with the one stored in record_path. If
   this has changed (or the record doesn't exist), function will be called and
   the new md5sum will be recorded.
 
   If force is True, the function will be called regardless of whether the
   md5sum is out of date.
   """
   if not input_paths:
     input_paths = []
   if not input_strings:
     input_strings = []
   md5_checker = _Md5Checker(
       record_path=record_path,
       input_paths=input_paths,
       input_strings=input_strings)
   if force or md5_checker.IsStale():
     function()
     md5_checker.Write()
+  elif _RECORD_EXTRA_INFO:
+    md5_checker.Write()
 
 
 def _UpdateMd5ForFile(md5, path, block_size=2**16):
   with open(path, 'rb') as infile:
     while True:
       data = infile.read(block_size)
       if not data:
         break
       md5.update(data)
 
@@ skipping 18 matching lines @@
     if not input_strings:
       input_strings = []
 
     assert record_path.endswith('.stamp'), (
         'record paths must end in \'.stamp\' so that they are easy to find '
         'and delete')
 
     self.record_path = record_path
 
     md5 = hashlib.md5()
+    extended_info = []
     for i in sorted(input_paths):
       _UpdateMd5ForPath(md5, i)
+      extended_info.append(i + '=' + md5.hexdigest())
+
     for s in input_strings:
       md5.update(s)
+      extended_info.append(s)
+
     self.new_digest = md5.hexdigest()
+    self.extended_info = extended_info
 
     self.old_digest = ''
     if os.path.exists(self.record_path):
       with open(self.record_path, 'r') as old_record:
-        self.old_digest = old_record.read()
+        for line in old_record:

[jbudorick, 2015/08/23 02:31:01]

self.old_digest = old_record.readline().strip()

?

+          self.old_digest = line.strip()
+          break
 
   def IsStale(self):
     return self.old_digest != self.new_digest
 
   def Write(self):
     with open(self.record_path, 'w') as new_record:
       new_record.write(self.new_digest)
+      if _RECORD_EXTRA_INFO:
+        new_record.write('\n' + '\n'.join(self.extended_info))