Add 32-bit iOS transition perf integration test (#17582)

dev/devicelab/manifest.yaml

diff --git a/dev/devicelab/manifest.yaml b/dev/devicelab/manifest.yaml
index c04b4c9..52aaf32 100644
--- a/dev/devicelab/manifest.yaml
+++ b/dev/devicelab/manifest.yaml
@@ -427,3 +427,11 @@
       Measures the speed of Dart analyzer.
     stage: devicelab
     required_agent_capabilities: ["linux/android"]
+
+  flutter_gallery_ios32__transition_perf:
+    description: >
+      Measures the performance of screen transitions in Flutter Gallery on
+      32-bit iOS.
+    stage: devicelab_ios
+    required_agent_capabilities: ["mac/ios32"]
+    flaky: true