Roll Flutter (stable) from 2e9cb0aa71a3 to 78666c8dc57e (1 revision) (#…

…5734)

flutter/flutter@2e9cb0a...78666c8

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-stable-packages
Please CC bmparr@google.com,rmistry@google.com,stuartmorgan@google.com on the revert to ensure that a human
is aware of the problem.

To file a bug in Flutter (stable): https://github.com/flutter/flutter/issues/new/choose
To file a bug in Packages: https://github.com/flutter/flutter/issues/new/choose

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Documentation for the AutoRoller is here:
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.ci/flutter_stable.version

@@ -1 +1 @@
-2e9cb0aa71a386a91f73f7088d115c0d96654829
+78666c8dc57e9f7548ca9f8dd0740fbf0c658dc9