mojo: Fix pathname2url being moved to urllib.request in Python 3

urllib.pathname2url() in Python 2.
urllib.request.pathname2url() in Python 3.
Use a custom module name and import depending on Python version.

Traceback (most recent call last):
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 556, in <module>
    sys.exit(main())
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 551, in main
    return args.func(args, remaining_args)
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 267, in _Generate
    processor._GenerateModule(args, remaining_args, generator_modules,
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 199, in _GenerateModule
    imports[parsed_imp.import_filename] = self._GenerateModule(
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 199, in _GenerateModule
    imports[parsed_imp.import_filename] = self._GenerateModule(
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 238, in _GenerateModule
    generator.GenerateFiles(filtered_args)
  File "C:\Google\chromium\src\mojo\public\tools\bindings\generators\mojom_js_generator.py", line 369, in GenerateFiles
    self.WriteWithComment(self._GenerateAMDModule(), "%s.js" % self.module.path)
  File "C:\Google\chromium\src\mojo\public\tools\bindings\pylib\mojom\generate\template_expander.py", line 37, in GeneratorInternal
    return ApplyTemplate(args[0], path_to_template, parameters, **kwargs)
  File "C:\Google\chromium\src\mojo\public\tools\bindings\pylib\mojom\generate\template_expander.py", line 30, in ApplyTemplate
    return template.render(params)
  File "C:\Google\chromium\src\mojo\public\tools\bindings\pylib\mojom\generate\..\..\..\..\..\..\..\third_party\jinja2\asyncsupport.py", line 76, in render
    return original_render(self, *args, **kwargs)
  File "C:\Google\chromium\src\mojo\public\tools\bindings\pylib\mojom\generate\..\..\..\..\..\..\..\third_party\jinja2\environment.py", line 1008, in render
    return self.environment.handle_exception(exc_info, True)
  File "C:\Google\chromium\src\mojo\public\tools\bindings\pylib\mojom\generate\..\..\..\..\..\..\..\third_party\jinja2\environment.py", line 780, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "C:\Google\chromium\src\mojo\public\tools\bindings\pylib\mojom\generate\..\..\..\..\..\..\..\third_party\jinja2\_compat.py", line 37, in reraise
    raise value.with_traceback(tb)
  File "gen\mojo\public\tools\bindings\js_templates.zip\tmpl_3ded8450c36dc0f89ab9459f617a5a73f83f3d2a.py", line 29, in <module>
  File "C:\Google\chromium\src\mojo\public\tools\bindings\generators\mojom_js_generator.py", line 218, in GetRelativeUrl
    return urllib.pathname2url(
AttributeError: module 'urllib' has no attribute 'pathname2url'

Bug: 941669
Change-Id: Icc7b07a75ba172bef11a949e2e6f22f50a690ca6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2046170Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Raul Tambre <raul@tambre.ee>
Cr-Commit-Position: refs/heads/master@{#740217}

mojo/public/tools/bindings/generators/mojom_js_generator.py

@@ -8,9 +8,14 @@ import mojom.generate.generator as generator
 import mojom.generate.module as mojom
 import mojom.generate.pack as pack
 import os
-import urllib
+import sys
 from mojom.generate.template_expander import UseJinja
 
+if sys.version_info.major == 2:
+  import urllib as urllib_request
+else:
+  import urllib.request as urllib_request
+
 _kind_to_javascript_default_value = {
   mojom.BOOL:                  "false",
   mojom.INT8:                  "0",
@@ -225,7 +230,7 @@ def GetArrayExpectedDimensionSizes(kind):
 
 
 def GetRelativeUrl(module, base_module):
-  return urllib.pathname2url(
+  return urllib_request.pathname2url(
       os.path.relpath(module.path, os.path.dirname(base_module.path)))