extract chunked detection into AIOHTTPSession._chunked()

aiobotocore/httpsession.py

@@ -135,6 +135,13 @@ def _setup_proxy_ssl_context(self, proxy_url):
         except (OSError, LocationParseError) as e:
             raise InvalidProxiesConfigError(error=e)
 
+    def _chunked(self, headers):
+        transfer_encoding = headers.get('Transfer-Encoding', '')
+        if chunked := transfer_encoding.lower() == 'chunked':
+            # aiohttp wants chunking as a param, and not a header
+            del headers['Transfer-Encoding']
+        return chunked
+
     def _create_connector(self, proxy_url):
         ssl_context = None
         if bool(self._verify):
@@ -208,12 +215,6 @@ async def send(self, request):
             # https://github.com/boto/botocore/issues/1255
             headers_['Accept-Encoding'] = 'identity'
 
-            chunked = None
-            if headers_.get('Transfer-Encoding', '').lower() == 'chunked':
-                # aiohttp wants chunking as a param, and not a header
-                headers_.pop('Transfer-Encoding', '')
-                chunked = True
-
             if isinstance(data, io.IOBase):
                 data = _IOBaseWrapper(data)
 
@@ -222,7 +223,7 @@ async def send(self, request):
             response = await session.request(
                 request.method,
                 url=url,
-                chunked=chunked,
+                chunked=self._chunked(headers_),
                 headers=headers_,
                 data=data,
                 proxy=proxy_url,