Fix autoninja to call ninja.py

ninja.exe will be removed from depot_tools soon.
Calling ninja.py finds the ninja installed by DEPS or one in PATH.

Bug: 1340825
Change-Id: I32ed6d8e5b0498347042490eedeca19972d35233
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4061247
Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Auto-Submit: Junji Watanabe <jwata@google.com>
Reviewed-by: Fumitoshi Ukai <ukai@google.com>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Junji Watanabe <jwata@google.com>

autoninja.py

@@ -168,11 +168,6 @@ def main(args):
           print('false')
         sys.exit(1)
 
-  # Specify ninja.exe on Windows so that ninja.bat can call autoninja and not
-  # be called back.
-  ninja_exe = 'ninja.exe' if sys.platform.startswith('win') else 'ninja'
-  ninja_exe_path = os.path.join(SCRIPT_DIR, ninja_exe)
-
   # A large build (with or without goma) tends to hog all system resources.
   # Launching the ninja process with 'nice' priorities improves this situation.
   prefix_args = []
@@ -182,9 +177,10 @@ def main(args):
     # ionice -c 3 is IO priority IDLE
     prefix_args = ['nice'] + ['-10']
 
-  # Use absolute path for ninja path,
+  # Call ninja.py so that it can find ninja binary installed by DEPS or one in
-  # or fail to execute ninja if depot_tools is not in PATH.
+  # PATH.
-  args = prefix_args + [ninja_exe_path] + input_args[1:]
+  ninja_path = os.path.join(SCRIPT_DIR, 'ninja.py')
+  args = prefix_args + [sys.executable, ninja_path] + input_args[1:]
 
   num_cores = multiprocessing.cpu_count()
   if not j_specified and not t_specified: