tools/run_node: only create 'node_modules' symlink once

Previously run_node.py would always attempt to remove and then re-create
the 'target/xx/node_modules' symlink. This causes sporadic build errors
on windows when multiple build targets that use run_node.py are being
built concurrently.

tools/run_node.py

@@ -5,15 +5,13 @@ gn can only run python scripts. This launches a subprocess Node process.
 The working dir of this program is out/Debug/ (AKA root_build_dir)
 Before running node, we symlink js/node_modules to out/Debug/node_modules.
 """
-import subprocess
 import sys
-import os
-from util import remove_and_symlink, root_path, run
+from os import path
+from util import symlink, root_path, run
 
-tools_path = os.path.join(root_path, "tools")
-third_party_path = os.path.join(root_path, "third_party")
-target_abs = os.path.join(third_party_path, "node_modules")
-target_rel = os.path.relpath(target_abs)
+if not path.exists("node_modules"):
+    target_abs = path.join(root_path, "third_party/node_modules")
+    target_rel = path.relpath(target_abs)
+    symlink(target_rel, "node_modules", True)
 
-remove_and_symlink(target_rel, "node_modules", True)
 run(["node"] + sys.argv[1:], quiet=True)

tools/util.py

@@ -93,20 +93,6 @@ def green_ok():
     return "%sok%s" % (FG_GREEN, RESET)
 
 
-def remove_and_symlink(target, name, target_is_dir=False):
-    if os.name != "nt" and os.path.islink(name):
-        return
-    try:
-        # On Windows, directory symlink can only be removed with rmdir().
-        if os.name == "nt" and os.path.isdir(name):
-            os.rmdir(name)
-        else:
-            os.unlink(name)
-    except OSError:
-        pass
-    symlink(target, name, target_is_dir)
-
-
 def symlink(target, name, target_is_dir=False):
     if os.name == "nt":
         from ctypes import WinDLL, WinError, GetLastError