Rewrite plugin_flags.sh Bash script in Python.

This is necessary because GN's exec_script only runs Python scripts.

This was requested by Nico in https://codereview.chromium.org/971593003/.

BUG=462972
TEST=run ./tools/clang/scripts/plugin_flags.py and compare the output
with the bash version. They should be exactly the same.
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/966723003

Cr-Commit-Position: refs/heads/master@{#318924}

build/common.gypi

@@ -2162,9 +2162,8 @@
         'enable_service_discovery%': 1
       }],
       ['clang_use_chrome_plugins==1 and OS!="win"', {
-        'clang_chrome_plugins_flags': [
-          '<!@(<(DEPTH)/tools/clang/scripts/plugin_flags.sh)'
-        ],
+        'clang_chrome_plugins_flags%':
+          '<!(python <(DEPTH)/tools/clang/scripts/plugin_flags.py)',
       }],
       ['asan==1 or msan==1 or lsan==1 or tsan==1', {
         'clang%': 1,

testing/buildbot/trybot_analyze_config.json

@@ -34,7 +34,7 @@
       "third_party/accessibility-audit/axs_testing.js",
       "third_party/hunspell_dictionaries/.*",
       "third_party/zlib/google/test/data/.*",
-      "tools/clang/scripts/plugin_flags.sh",
+      "tools/clang/scripts/plugin_flags.py",
       "tools/clang/scripts/update.py",
       "tools/clang/scripts/update.sh",
       "tools/metrics/histograms/histograms.xml",

tools/clang/scripts/plugin_flags.py

+#!/usr/bin/env python
+# Copyright 2015 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.
+
+# This script returns the flags that should be used when GYP_DEFINES contains
+# clang_use_chrome_plugins. The flags are stored in a script so that they can
+# be changed on the bots without requiring a master restart.
+
+import os
+import sys
+
+# Path constants. (All of these should be absolute paths.)
+THIS_DIR = os.path.abspath(os.path.dirname(__file__))
+CHROMIUM_DIR = os.path.abspath(os.path.join(THIS_DIR, '..', '..', '..'))
+CLANG_LIB_PATH = os.path.join(CHROMIUM_DIR, 'third_party', 'llvm-build',
+                              'Release+Asserts', 'lib')
+
+if sys.platform == 'darwin':
+  LIBSUFFIX = 'dylib'
+else:
+  LIBSUFFIX = 'so'
+
+LIB_PATH = os.path.join(
+    CLANG_LIB_PATH,
+    'libFindBadConstructs.' + LIBSUFFIX)
+
+print ('-Xclang -load -Xclang %s'
+       ' -Xclang -add-plugin -Xclang find-bad-constructs'
+       ' -Xclang -plugin-arg-find-bad-constructs'
+       ' -Xclang check-weak-ptr-factory-order'
+       ' -Xclang -plugin-arg-find-bad-constructs'
+       ' -Xclang strict-virtual-specifiers') % LIB_PATH

tools/clang/scripts/plugin_flags.sh

-#!/usr/bin/env bash
-# Copyright (c) 2012 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.
-
-# This script returns the flags that should be used when GYP_DEFINES contains
-# clang_use_chrome_plugins. The flags are stored in a script so that they can
-# be changed on the bots without requiring a master restart.
-
-SRC_ABS_DIR=$(cd $(dirname $0)/../../.. && echo $PWD)
-CLANG_LIB_PATH=$SRC_ABS_DIR/third_party/llvm-build/Release+Asserts/lib
-
-if uname -s | grep -q Darwin; then
-  LIBSUFFIX=dylib
-else
-  LIBSUFFIX=so
-fi
-
-echo -Xclang -load -Xclang $CLANG_LIB_PATH/libFindBadConstructs.$LIBSUFFIX \
-  -Xclang -add-plugin -Xclang find-bad-constructs