Preparing v8 to use with python3

There are now less that 100 days until the end of life
of Python 2(aka _legacy_ Python) https://pythonclock.org/ .
The code compatibility check for python2 and python3
used the following tools: futurize, flake8

Related tasks:
1. https://github.com/nodejs/node/issues/24512
2. https://github.com/v8/v8/pull/35

Bug: v8:8594
Change-Id: Ia081a158a2b41cd880a5d47bb340f21858340d42
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1864942
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64381}

test/preparser/testcfg.py

@@ -66,7 +66,9 @@ class TestSuite(testsuite.TestSuite):
           testsource = testsource.replace("$" + key, replacement[key]);
         Test(testname, testsource, expectation)
       return MkTest
-    execfile(pathname, {"Test": Test, "Template": Template})
+    with open(pathname) as f:
+      text = f.read()
+    exec(text, {"Test": Test, "Template": Template})
 
   def ListTests(self):
     result = []

tools/regexp-sequences.py

@@ -24,7 +24,7 @@ def parse(file, seqlen):
                   r'(:?\.|\()(?P<char>\.|\w)(:?\.|\)), bc = (?P<bc>\w+), .*')
   total = 0
   bc_cnt = [None] * seqlen
-  for i in xrange(seqlen):
+  for i in range(seqlen):
     bc_cnt[i] = {}
   last = [None] * seqlen
   with open(file) as f:
@@ -32,14 +32,14 @@ def parse(file, seqlen):
     while l:
       l = l.strip()
       if l.startswith("Start bytecode interpreter"):
-        for i in xrange(seqlen):
+        for i in range(seqlen):
           last[i] = collections.deque(maxlen=i+1)
 
       match = rx.search(l)
       if match:
         total += 1
         bc = match.group('bc')
-        for i in xrange(seqlen):
+        for i in range(seqlen):
           last[i].append(bc)
           key = ' --> '.join(last[i])
           bc_cnt[i][key] = bc_cnt[i].get(key,0) + 1
@@ -57,7 +57,7 @@ def print_most_common(d, seqlen, total):
 def main(argv):
   max_seq = 7
   bc_cnt, total = parse(argv[1],max_seq)
-  for i in xrange(max_seq):
+  for i in range(max_seq):
     print()
     print("Most common of length {}".format(i+1))
     print()

tools/wasm-compilation-hints/wasm-objdump-compilation-hints.py

@@ -4,6 +4,7 @@
 # Use of this source code is governed by a BSD-style license that can be found
 # in the LICENSE file.
 
+from __future__ import print_function
 import argparse
 import io
 import sys
@@ -34,10 +35,10 @@ if __name__ == "__main__":
         section_name_bs = fin.read(section_name_length)
         if section_name_bs == "compilationHints":
           num_hints, bs = read_varuintN(fin)
-          print "Custom section compilationHints with", num_hints, "hints:"
+          print("Custom section compilationHints with ", num_hints, "hints:")
           for i in range(num_hints):
             hint, bs = read_uint8(fin)
-            print i, hex(hint)
+            print(i, " ", hex(hint))
         else:
           remaining_length = payload_length \
               - len(section_name_length_bs) \