feat(storage): set auto-decompress as needed for download_stream

Fixes talkiq#988

Author: TheKevJames

storage/gcloud/aio/storage/storage.py

@@ -671,6 +671,16 @@ async def _download_stream(
         headers = headers or {}
         headers.update(await self._headers())
 
+        # aiohttp and requests automatically decompress the body if this
+        # argument is not passed, unless a user has explicitly disabled that
+        # option at the session level in the case of aiohttp. We follow the
+        # user setting by default (by passing None) and only explicitly disable
+        # it when we know that the object is not compressed (when the
+        # Accept-Encoding header is missing).
+        auto_decompress = None
+        if 'accept-encoding' not in {k.lower() for k in headers}:
+            auto_decompress = False
+
         s = AioSession(session) if session else self.session
 
         if BUILD_GCLOUD_REST:
@@ -685,7 +695,7 @@ async def _download_stream(
         return StreamResponse(
             await s.get(
                 url, headers=headers, params=params or {},
-                timeout=timeout,
+                timeout=timeout, auto_decompress=auto_decompress,
             ),
         )