Add startup test for Platform View example (#17645)

dev/devicelab/manifest.yaml

diff --git a/dev/devicelab/manifest.yaml b/dev/devicelab/manifest.yaml
index 52aaf32..3d5f4e4 100644
--- a/dev/devicelab/manifest.yaml
+++ b/dev/devicelab/manifest.yaml
@@ -136,6 +136,12 @@
     stage: devicelab
     required_agent_capabilities: ["mac/android"]
 
+  platform_view__start_up:
+    description: >
+      Verifies that Platform View can be used from an Android project.
+    stage: devicelab
+    required_agent_capabilities: ["mac/android"]
+
   complex_layout__start_up:
     description: >
       Measures the startup time of the Complex Layout sample app on Android.
@@ -289,6 +295,12 @@
     stage: devicelab_ios
     required_agent_capabilities: ["mac/ios"]
 
+  platform_view_ios__start_up:
+    description: >
+      Verifies that Platform View can be used from an iOS project.
+    stage: devicelab_ios
+    required_agent_capabilities: ["mac/ios"]
+
   complex_layout_scroll_perf_ios__timeline_summary:
     description: >
       Measures the runtime performance of the Complex Layout sample app on