Roll Flutter from 99475b1b0bee to b55bbb7bffc7 (36 revisions) (#2624)

diff --git a/.ci/flutter_master.version b/.ci/flutter_master.version
index a9baeda..0371be1 100644
--- a/.ci/flutter_master.version
+++ b/.ci/flutter_master.version
@@ -1 +1 @@
-99475b1b0bee6ab09d0282b255c6b8c7e01ca4fe
+b55bbb7bffc79adf9cce33ebda0582df41aae280