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

build/android/gyp/util/md5_check.py

Index: build/android/gyp/util/md5_check.py
diff --git a/build/android/gyp/util/md5_check.py b/build/android/gyp/util/md5_check.py
index 9f365aa08162c83b22192b675a1a53a5e9acb87f..14ba8f1d96dc6fbbcc6b719d2fa28eea9ee73692 100644
--- a/build/android/gyp/util/md5_check.py
+++ b/build/android/gyp/util/md5_check.py
@@ -6,6 +6,11 @@ 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):
@@ -29,6 +34,8 @@ def CallAndRecordIfStale(
   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):
@@ -67,16 +74,24 @@ class _Md5Checker(object):
     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
@@ -84,3 +99,5 @@ class _Md5Checker(object):
   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))