Remove disable of GZIP, as it's no longer on by default anymore.

sdk/lib/_internal/pub/lib/src/barback/base_server.dart

Index: sdk/lib/_internal/pub/lib/src/barback/base_server.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/base_server.dart b/sdk/lib/_internal/pub/lib/src/barback/base_server.dart
index cb23036f17a79bbabab63bc4133e68809c74d13c..a47b362f962efc7d9e9e08f33c1d5d8a0e0781d1 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/base_server.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/base_server.dart
@@ -44,7 +44,6 @@ abstract class BaseServer<T> {
   BaseServer(this.environment, this._server) {
     shelf_io.serveRequests(_server, const shelf.Pipeline()
         .addMiddleware(shelf.createMiddleware(errorHandler: _handleError))
-        .addMiddleware(shelf.createMiddleware(responseHandler: _disableGzip))
         .addHandler(handleRequest));
   }
 
@@ -121,20 +120,4 @@ abstract class BaseServer<T> {
     close();
     return new shelf.Response.internalServerError();
   }
-
-  /// Disable GZIP responses.
-  ///
-  /// This is primarily to optimize pub's startup. Since the transformer
-  /// plug-ins are loaded over HTTP, we pay the hit to GZIP encode and decode
-  /// them. Disabling this improves startup time by about 5% on my test.
-  ///
-  // TODO(rnystrom): Remove this when #5187 is fixed and we don't have to use
-  // HTTP for isolates.
-  _disableGzip(shelf.Response response) {
-    if (!response.headers.containsKey('Content-Encoding')) {
-      return response.change(headers: {'Content-Encoding': ''});
-    }
-
-    return response;
-  }
 }