Roll Flutter from 03c92a99fdf8 to a491a81f7873 (26 revisions) (#5014)

diff --git a/.ci/flutter_master.version b/.ci/flutter_master.version
index 4eb3f36..d34ceb4 100644
--- a/.ci/flutter_master.version
+++ b/.ci/flutter_master.version
@@ -1 +1 @@
-03c92a99fdf8d91db89fa8dde19912b7ef341b67
+a491a81f78739dc1c801529b98239adc6a2dd361