[code coverage] Enable 3% CQ experiment for ios-simulator-code-coverage

Will observe if there are issues from the experiment then set code
coverage as default in iOS CQ builders.

Bug: 1090188
Change-Id: I77e58aefbfc4964f63de61cef7bd7a351d11bfc7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2227236
Commit-Queue: Zhaoyang Li <zhaoyangli@chromium.org>
Reviewed-by: Garrett Beaty <gbeaty@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774443}

infra/config/generated/commit-queue.cfg

@@ -730,7 +730,7 @@ config_groups: <
       >
       builders: <
         name: "chromium/try/ios-simulator-code-coverage"
-        includable_only: true
+        experiment_percentage: 3
       >
       builders: <
         name: "chromium/try/ios-simulator-cr-recipe"

infra/config/generated/cq-builders.md

@@ -339,6 +339,9 @@ as required builders.
 * [fuchsia-compile-x64-dbg](https://ci.chromium.org/p/chromium/builders/try/fuchsia-compile-x64-dbg) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+fuchsia-compile-x64-dbg)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+fuchsia-compile-x64-dbg))
   * Experiment percentage: 50
 
+* [ios-simulator-code-coverage](https://ci.chromium.org/p/chromium/builders/try/ios-simulator-code-coverage) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+ios-simulator-code-coverage)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+ios-simulator-code-coverage))
+  * Experiment percentage: 3
+
 * [linux-perfetto-rel](https://ci.chromium.org/p/chromium/builders/try/linux-perfetto-rel) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+linux-perfetto-rel)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+linux-perfetto-rel))
   * Experiment percentage: 100
 

infra/config/subprojects/chromium/master-only/try.star

@@ -574,6 +574,7 @@ try_.chromium_mac_ios_builder(
     properties = {
         'xcode_build_version': '11e146',
     },
+    tryjob = try_.job(experiment_percentage = 3)
 )
 
 try_.chromium_mac_ios_builder(