Support Python 3 in //tools/js2c.py

The script still works with Python 2.
There are no intended behaviour changes.

Bug: chromium:941669
Change-Id: I5ec63564fdb29a326c64d6ac7465f86b30ef16c1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1585857Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Auto-Submit: Raul Tambre <raul@tambre.ee>
Cr-Commit-Position: refs/heads/master@{#61191}

AUTHORS

@@ -148,6 +148,7 @@ PhistucK <phistuck@gmail.com>
 Qingyan Li <qingyan.liqy@alibaba-inc.com>
 Qiuyi Zhang <qiuyi.zqy@alibaba-inc.com>
 Rafal Krypa <rafal@krypa.net>
+Raul Tambre <raul@tambre.ee>
 Ray Glover <ray@rayglover.net>
 Refael Ackermann <refack@gmail.com>
 Rene Rebe <rene@exactcode.de>

tools/js2c.py

@@ -245,7 +245,10 @@ def BuildMetadata(sources, source_bytes, native_type):
   raw_sources = "".join(sources.modules)
 
   # The sources are expected to be ASCII-only.
-  assert not filter(lambda value: ord(value) >= 128, raw_sources)
+  try:
+    raw_sources.encode('ascii')
+  except UnicodeEncodeError:
+    assert False
 
   # Loop over modules and build up indices into the source blob:
   get_index_cases = []
@@ -300,8 +303,8 @@ def PutInt(blob_file, value):
 
 
 def PutStr(blob_file, value):
-  PutInt(blob_file, len(value));
-  blob_file.write(value);
+  PutInt(blob_file, len(value.encode()))
+  blob_file.write(value.encode())
 
 
 def WriteStartupBlob(sources, startup_blob):