[flutter_tools] fast start off by default (flutter#49554)

Author: Jonah Williams

packages/flutter_tools/lib/src/commands/run.dart

@@ -187,9 +187,12 @@ class RunCommand extends RunCommandBase {
         hide: true,
         help: 'Whether to automatically invoke webOnlyInitializePlatform.',
       )
+      // TODO(jonahwilliams): Off by default with investigating whether this
+      // is slower for certain use cases.
+      // See: https://github.com/flutter/flutter/issues/49499
       ..addFlag('fast-start',
         negatable: true,
-        defaultsTo: true,
+        defaultsTo: false,
         help: 'Whether to quickly bootstrap applications with a minimal app. '
               'Currently this is only supported on Android devices. This option '
               'cannot be paired with --use-application-binary.'