Bug 1305877 - Make HashChunker stable; r=jgraham

The built-in hash() function uses the backing memory address for
hashing. This is essentially random. Switch to md5 so input is
consistently hashed across processes.

MozReview-Commit-ID: D52uzttE5hc

--HG--
extra : rebase_source : b7f15e519ec0ba05d0a310fe0470d82893a0a07c
extra : source : 4c8e1c96a27df961c1dd2e984745d06757e8a2d4

testing/web-platform/harness/wptrunner/testloader.py

@@ -1,6 +1,6 @@
+import hashlib
 import json
 import os
-import sys
 import urlparse
 from abc import ABCMeta, abstractmethod
 from Queue import Empty
@@ -43,12 +43,14 @@ class Unchunked(TestChunker):
 
 
 class HashChunker(TestChunker):
-    def __call__(self):
+    def __call__(self, manifest):
         chunk_index = self.chunk_number - 1
         for test_path, tests in manifest:
-            if hash(test_path) % self.total_chunks == chunk_index:
+            h = int(hashlib.md5(test_path).hexdigest(), 16)
+            if h % self.total_chunks == chunk_index:
                 yield test_path, tests
 
+
 class EqualTimeChunker(TestChunker):
     def _group_by_directory(self, manifest_items):
         """Split the list of manifest items into a ordered dict that groups tests in