Fix copy-paste error on dir check

It was still using path, but that is an import. Instead, we should use
the proper computed directory

Change-Id: I5b606f61361082c71d0307225490b98db7d9e8c1
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2078928
Auto-Submit: Tim van der Lippe <tvanderlippe@chromium.org>
Reviewed-by: Jack Franklin <jacktfranklin@chromium.org>
Commit-Queue: Tim van der Lippe <tvanderlippe@chromium.org>

third_party/typescript/ts_library.py

@@ -109,10 +109,11 @@ def copy_all_typescript_sources(sources, output_directory):
                 os.remove(dest)
             # Make sure that the directory actually exists, otherwise
             # the copy action will throw an error
+            dest_directory = path.dirname(dest)
             try:
-                os.makedirs(path.dirname(dest))
+                os.makedirs(dest_directory)
             except OSError as exc:  # Python >2.5
-                if exc.errno == errno.EEXIST and os.path.isdir(path):
+                if exc.errno == errno.EEXIST and os.path.isdir(dest_directory):
                     pass
                 else:
                     raise