Roll Flutter from c849844feb3d to 54a9d6528289 (1 revision) (#4900)

diff --git a/.ci/flutter_master.version b/.ci/flutter_master.version
index 2eebe0e..10b0279 100644
--- a/.ci/flutter_master.version
+++ b/.ci/flutter_master.version
@@ -1 +1 @@
-c849844feb3de477b27dfcb3bd6879ca621bccc7
+54a9d652828941dbebbe8de32cf667e89578b13d