Accept non utf-8 characters with python3

If input file contains non-utf-8 characters, running
GetResourceAllowlistFileList in python3 fails with a variation of:
"UnicodeDecodeError: 'utf-8' codec can't decode byte 0x80 in position 24: invalid start byte"

This change makes python3 treat data as bytes, while leaving
python2 behavior unchanged.

Change-Id: Idb6f4cf8fe3a98551df91b1249a1b74ba2916acc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2560505Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#831015}

tools/resources/generate_resource_allowlist.py

@@ -111,15 +111,15 @@ def GetResourceAllowlistFileList(file_list_path):
   paths = ar.ExpandThinArchives(paths)
 
   resource_ids = set()
-  prefix = 'AllowlistedResource<'
+  prefix = b'AllowlistedResource<'
   for p in paths:
-    with open(p) as f:
+    with open(p, 'rb') as f:
       data = f.read()
     start_idx = 0
     while start_idx != -1:
       start_idx = data.find(prefix, start_idx)
       if start_idx != -1:
-        end_idx = data.find('>', start_idx)
+        end_idx = data.find(b'>', start_idx)
         resource_ids.add(int(data[start_idx + len(prefix):end_idx]))
         start_idx = end_idx
   return resource_ids