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>
diff --git a/generator/dawn_json_generator.py b/generator/dawn_json_generator.py
index 37ad05d..6037aa8 100644
--- a/generator/dawn_json_generator.py
+++ b/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");
diff --git a/generator/extract_json.py b/generator/extract_json.py
index 40312f9..4afefae 100644
--- a/generator/extract_json.py
+++ b/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");
diff --git a/generator/generator_lib.py b/generator/generator_lib.py
index bda4c1e..8deec5d 100644
--- a/generator/generator_lib.py
+++ b/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");
diff --git a/generator/opengl_loader_generator.py b/generator/opengl_loader_generator.py
index 1ed148a..47721e2 100644
--- a/generator/opengl_loader_generator.py
+++ b/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");
diff --git a/generator/remove_files.py b/generator/remove_files.py
index b143abe..0b8b521 100644
--- a/generator/remove_files.py
+++ b/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");
diff --git a/scripts/perf_test_runner.py b/scripts/perf_test_runner.py
index 546bebd..c4cc55c 100755
--- a/scripts/perf_test_runner.py
+++ b/scripts/perf_test_runner.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python2
+#!/usr/bin/env python3
 #
 # Copyright 2019 The Dawn Authors
 #