Use python3 for all of Dawn's python scripts

Bug: dawn:389
Change-Id: I5034ab2791f0cca0b7690eae5f4d7f4e6efc4bd9
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/19863
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

generator/dawn_json_generator.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # Copyright 2017 The Dawn Authors
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

generator/extract_json.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # Copyright 2018 The Dawn Authors
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

generator/generator_lib.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # Copyright 2019 The Dawn Authors
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

generator/opengl_loader_generator.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # Copyright 2019 The Dawn Authors
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

generator/remove_files.py

@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 # Copyright 2019 The Dawn Authors
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

scripts/perf_test_runner.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python2
+#!/usr/bin/env python3
 #
 # Copyright 2019 The Dawn Authors
 #