Roll Flutter from b5321d182a6b to 78eb916d1516 (1 revision) (#1744)

diff --git a/.ci/flutter_master.version b/.ci/flutter_master.version
index b287617..fb8a902 100644
--- a/.ci/flutter_master.version
+++ b/.ci/flutter_master.version
@@ -1 +1 @@
-b5321d182a6bf89fd3d86ceee52179867ffa7c89
+78eb916d15160a2fa9a1b27c812b7c620c27e3ae