Switch all 'python' strings to input_api.python_executable in PRESUBMIT.py

This guarantees that the same python runtime is used throughput the presubmit
checks. This also saves an unnecessary cmd.exe process on Windows, which saves a
few ms.

TBR=vadimsh@chromium.org
BUG=761523

Change-Id: I32ef6966fbd33835ec9d4d9d4a9628d759c86884
Reviewed-on: https://chromium-review.googlesource.com/648446Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>
Commit-Queue: Marc-Antoine Ruel <maruel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#499496}

tools/checkteamtags/PRESUBMIT.py

@@ -8,8 +8,6 @@ See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts for
 details on the presubmit API.
 """
 
-import subprocess
-
 
 def CheckChangeOnUpload(input_api, output_api):
   return _CommonChecks(input_api, output_api)
@@ -26,13 +24,15 @@ def _CommonChecks(input_api, output_api):
   results.extend(_RunPyLint(input_api, output_api))
   return results
 
+
 def _RunUnitTests(input_api, output_api):
   """Runs unit tests for checkteamtags."""
   repo_root = input_api.change.RepositoryRoot()
   checkteamtags_dir = input_api.os_path.join(repo_root, 'tools',
                                              'checkteamtags')
   test_runner = input_api.os_path.join(checkteamtags_dir, 'run_tests')
-  return_code = subprocess.call(['python', test_runner])
+  return_code = input_api.subprocess.call(
+      [input_api.python_executable, test_runner])
   if return_code:
     message = 'Checkteamtags unit tests did not all pass.'
     return [output_api.PresubmitError(message)]

tools/metrics/actions/PRESUBMIT.py

@@ -17,7 +17,8 @@ def CheckChange(input_api, output_api):
         and input_api.os_path.dirname(p) == input_api.PresubmitLocalPath()):
       cwd = input_api.os_path.dirname(p)
       exit_code = input_api.subprocess.call(
-          ['python', 'extract_actions.py', '--presubmit'], cwd=cwd)
+          [input_api.python_executable, 'extract_actions.py', '--presubmit'],
+          cwd=cwd)
       if exit_code != 0:
         return [output_api.PresubmitError(
             'actions.xml is not up to date or is not formatted correctly; '

tools/metrics/histograms/PRESUBMIT.py

@@ -25,7 +25,8 @@ def CheckChange(input_api, output_api):
     cwd = input_api.PresubmitLocalPath()
 
     exit_code = input_api.subprocess.call(
-        ['python', 'pretty_print.py', '--presubmit', '--non-interactive'],
+        [input_api.python_executable, 'pretty_print.py', '--presubmit',
+         '--non-interactive'],
         cwd=cwd)
     if exit_code != 0:
       results.append(output_api.PresubmitError(
@@ -33,7 +34,7 @@ def CheckChange(input_api, output_api):
           'git cl format %s to fix.' % cwd))
 
     exit_code = input_api.subprocess.call(
-        ['python', 'validate_format.py'], cwd=cwd)
+        [input_api.python_executable, 'validate_format.py'], cwd=cwd)
     if exit_code != 0:
       results.append(output_api.PresubmitError(
           'histograms.xml is not well formatted; run %s/validate_format.py '

tools/metrics/rappor/PRESUBMIT.py

@@ -17,7 +17,8 @@ def CheckChange(input_api, output_api):
         and input_api.os_path.dirname(p) == input_api.PresubmitLocalPath()):
       cwd = input_api.os_path.dirname(p)
       exit_code = input_api.subprocess.call(
-          ['python', 'pretty_print.py', '--presubmit'], cwd=cwd)
+          [input_api.python_executable, 'pretty_print.py', '--presubmit'],
+          cwd=cwd)
       if exit_code != 0:
         return [output_api.PresubmitError(
             'rappor.xml is not formatted correctly; run %s/pretty_print.py '

tools/metrics/ukm/PRESUBMIT.py

@@ -19,7 +19,8 @@ def CheckChange(input_api, output_api):
         and input_api.os_path.dirname(p) == input_api.PresubmitLocalPath()):
       cwd = input_api.os_path.dirname(p)
       exit_code = input_api.subprocess.call(
-          ['python', 'pretty_print.py', '--presubmit'], cwd=cwd)
+          [input_api.python_executable, 'pretty_print.py', '--presubmit'],
+          cwd=cwd)
       if exit_code != 0:
         return [output_api.PresubmitError(
             '%s is not formatted correctly; run %s/pretty_print.py to fix' %