autoninja: use pure python3 to get build id and for post_build_ninja_summary.py

This is for comments in
https://crrev.com/c/2629087/11/autoninja
and
https://crrev.com/c/2629087/11/autoninja.bat

Change-Id: I2edafaee7916b7c826af7a7f8f0150a541c8d098
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2631396Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@google.com>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>

autoninja

@@ -5,7 +5,7 @@
 # found in the LICENSE file.
 
 # Set unique build ID.
-AUTONINJA_BUILD_ID="$(vpython -c "import uuid; print(uuid.uuid4())")"
+AUTONINJA_BUILD_ID="$(python3 -c "import uuid; print(uuid.uuid4())")"
 export AUTONINJA_BUILD_ID
 
 if [ "$NINJA_SUMMARIZE_BUILD" == "1" ]; then
@@ -20,7 +20,7 @@ if [ "$NINJA_SUMMARIZE_BUILD" == "1" ]; then
 fi
 if eval "$command"; then
   if [ "$NINJA_SUMMARIZE_BUILD" == "1" ]; then
-    vpython "$(dirname -- "$0")/post_build_ninja_summary.py" "$@"
+    python3 "$(dirname -- "$0")/post_build_ninja_summary.py" "$@"
   fi
 
   # Collect ninjalog from googler.

autoninja.bat

@@ -6,7 +6,7 @@
 setlocal
 
 REM Set unique build ID.
-FOR /f "usebackq tokens=*" %%a in (`python -c "from __future__ import print_function; import uuid; print(uuid.uuid4())"`) do set AUTONINJA_BUILD_ID=%%a
+FOR /f "usebackq tokens=*" %%a in (`python3 -c "import uuid; print(uuid.uuid4())"`) do set AUTONINJA_BUILD_ID=%%a
 
 REM If a build performance summary has been requested then also set NINJA_STATUS
 REM to trigger more verbose status updates. In particular this makes it possible
@@ -37,7 +37,7 @@ FOR /f "usebackq tokens=*" %%a in (`vpython %scriptdir%autoninja.py "%*"`) do ec
 @if errorlevel 1 goto buildfailure
 
 REM Use call to invoke vpython script here, because we use vpython via vpython.bat.
-@if "%NINJA_SUMMARIZE_BUILD%" == "1" call vpython.bat %scriptdir%post_build_ninja_summary.py %*
+@if "%NINJA_SUMMARIZE_BUILD%" == "1" call python3 %scriptdir%post_build_ninja_summary.py %*
 @call python.bat %scriptdir%ninjalog_uploader_wrapper.py --cmdline %*
 
 exit /b

post_build_ninja_summary.py

-#!/usr/bin/env vpython
+#!/usr/bin/env python3
 # Copyright (c) 2018 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
@@ -17,7 +17,7 @@ $ NINJA_SUMMARIZE_BUILD=1 autoninja -C out/Default/ chrome
 You can also call this script directly using ninja's syntax to specify the
 output directory of interest:
 
-> python post_build_ninja_summary.py -C out/Default
+> python3 post_build_ninja_summary.py -C out/Default
 
 Typical output looks like this:
 
@@ -51,8 +51,6 @@ will have a weighted time that is the same or similar to its elapsed time. A
 compile that runs in parallel with 999 other compiles will have a weighted time
 that is tiny."""
 
-from __future__ import print_function
-
 import argparse
 import errno
 import fnmatch