Make the downloaded tarfile a dotfile

This is so that the third_party directories can gitignore the
downloaded tarfile. Currently theyre ignoring on *tar.gz

Bug: b/324418194
Change-Id: Id4aeeec366de3a0cec410de6ddd63369a3a4680a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5454165
Reviewed-by: Joanna Wang <jojwang@chromium.org>
Commit-Queue: Stephanie Kim <kimstephanie@google.com>

gclient.py

@@ -2650,7 +2650,7 @@ class GcsDependency(Dependency):
         # Directory of the extracted tarfile contents
         output_dir = os.path.join(root_dir, self.name.split(':')[0])
         output_file = os.path.join(output_dir, self.output_file
-                                   or gcs_file_name)
+                                   or f'.{gcs_file_name}')
 
         # Remove any forward slashes and drop any extensions
         file_prefix = self.object_name.replace('/', '_').split('.')[0]

tests/gclient_gcs_smoketest.py

@@ -35,12 +35,8 @@ class GClientSmokeGcs(gclient_smoketest_base.GClientSmokeBase):
 
         tree = self.mangle_git_tree(('repo_22@1', 'src'))
         tree.update({
-            'src/another_gcs_dep/llvmfile.tar.gz':
-            'tarfile',
             'src/another_gcs_dep/extracted_dir/extracted_file':
             'extracted text',
-            'src/gcs_dep/deadbeef':
-            'tarfile',
             'src/gcs_dep/extracted_dir/extracted_file':
             'extracted text',
             'src/gcs_dep_with_output_file/clang-format-no-extract':