Add support for GCS deps

Also take out GCS calling logic from download_google_storage and
into call_google_storage.

GCS deps look like:
   'src/third_party/node/linux': {
       'dep_type': 'gcs',
       'condition': 'checkout_linux',
       'bucket': 'chromium-nodejs/20.11.0',
       'object_name': '46795170ff5df9831955f163f6966abde581c8af',
       'sha256sum': '887504c37404898ca41b896f448ee6d7fc24179d8fb6a4b79d028ab7e1b7153d',
   },

   'src/third_party/llvm-build/Release+Asserts': {
       'dep_type': 'gcs',
       'condition': 'checkout_linux',
       'bucket': 'chromium-browser-clang',
       'object_name': 'Linux_x64/clang-llvmorg-18-init-17730-gf670112a-2.tar.xz',
       'sha256sum': '1e46df9b4e63c074064d75646310cb76be2f19815997a8486987189d80f991e8',
   },

Example directory for src/third_party/node/linux after gclient sync:
- tar_file.gz is the downloaded file from GCS.
- node_linux_x64/ is extracted in its path.
- `hash` contains the sha of GCS filename.
```
chromium/src/ ->
   third_party/node/linux/ ->
       hash, tar_file.gz, node_linux_x64/
```

Bug: b/324418194
Change-Id: Ibcbbff27e211f194ddb8a08494af56570a84a12b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5299722
Commit-Queue: Stephanie Kim <kimstephanie@google.com>
Reviewed-by: Joanna Wang <jojwang@chromium.org>

gclient_scm.py

@@ -1913,6 +1913,57 @@ class CipdWrapper(SCMWrapper):
     """
 
 
+class GcsWrapper(SCMWrapper):
+    """Wrapper for GCS.
+
+  Currently only supports content from Google Cloud Storage.
+  """
+    name = 'gcs'
+
+    def __init__(self,
+                 url=None,
+                 root_dir=None,
+                 relpath=None,
+                 out_fh=None,
+                 out_cb=None):
+        super(GcsWrapper, self).__init__(url=url,
+                                         root_dir=root_dir,
+                                         relpath=relpath,
+                                         out_fh=out_fh,
+                                         out_cb=out_cb)
+
+    #override
+    def GetCacheMirror(self):
+        return None
+
+    #override
+    def GetActualRemoteURL(self, options):
+        return None
+
+    #override
+    def DoesRemoteURLMatch(self, options):
+        del options
+        return True
+
+    def revert(self, options, args, file_list):
+        """Does nothing."""
+
+    def diff(self, options, args, file_list):
+        """GCS has no notion of diffing."""
+
+    def pack(self, options, args, file_list):
+        """GCS has no notion of diffing."""
+
+    def revinfo(self, options, args, file_list):
+        """Does nothing"""
+
+    def status(self, options, args, file_list):
+        pass
+
+    def update(self, options, args, file_list):
+        """Does nothing."""
+
+
 class CogWrapper(SCMWrapper):
     """Wrapper for Cog, all no-op."""
     name = 'cog'