bind-gen: Attempt to fix a build failure on a certain Win env, part 2

Preserves sys.path[0] as is just in case.

Bug: 839389, 1046970
Change-Id: I6904ff831783693720e6ee5e9597e7f40f7df683
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2041111Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738893}

third_party/blink/renderer/bindings/scripts/bind_gen/__init__.py

@@ -15,7 +15,7 @@ def _setup_sys_path():
     root_dir = os.path.abspath(
         os.path.join(this_dir, *(['..'] * expected_path.count('/'))))
 
-    sys.path = [
+    module_dirs = (
         # //third_party/blink/renderer/bindings/scripts/web_idl
         os.path.join(root_dir, 'third_party', 'blink', 'renderer', 'bindings',
                      'scripts'),
@@ -24,7 +24,11 @@ def _setup_sys_path():
                      'scripts'),
         # //third_party/mako/mako
         os.path.join(root_dir, 'third_party', 'mako'),
-    ] + sys.path
+    )
+    for module_dir in reversed(module_dirs):
+        # Preserve sys.path[0] as is.
+        # https://docs.python.org/3/library/sys.html?highlight=path[0]#sys.path
+        sys.path.insert(1, module_dir)
 
 
 _setup_sys_path()

third_party/blink/renderer/bindings/scripts/web_idl/__init__.py

@@ -15,7 +15,7 @@ def _setup_sys_path():
     root_dir = os.path.abspath(
         os.path.join(this_dir, *(['..'] * expected_path.count('/'))))
 
-    sys.path = [
+    module_dirs = (
         # //third_party/blink/renderer/build/scripts/blinkbuild
         os.path.join(root_dir, 'third_party', 'blink', 'renderer', 'build',
                      'scripts'),
@@ -25,7 +25,11 @@ def _setup_sys_path():
         os.path.join(root_dir, 'third_party', 'pyjson5', 'src'),
         # //tools/idl_parser
         os.path.join(root_dir, 'tools'),
-    ] + sys.path
+    )
+    for module_dir in reversed(module_dirs):
+        # Preserve sys.path[0] as is.
+        # https://docs.python.org/3/library/sys.html?highlight=path[0]#sys.path
+        sys.path.insert(1, module_dir)
 
 
 _setup_sys_path()