ensure default value for report timings (#52978)

diff --git a/packages/flutter_tools/lib/src/aot.dart b/packages/flutter_tools/lib/src/aot.dart
index 788cade..4c29daa 100644
--- a/packages/flutter_tools/lib/src/aot.dart
+++ b/packages/flutter_tools/lib/src/aot.dart
@@ -30,7 +30,7 @@
     bool bitcode = kBitcodeEnabledDefault,
     bool quiet = true,
     Iterable<DarwinArch> iosBuildArchs = defaultIOSArchs,
-    bool reportTimings,
+    bool reportTimings = false,
   }) async {
     if (platform == null) {
       throwToolExit('No AOT build platform specified');