emulator: Enable MM on CQ with 2 percent experimentally

According to estimation, 2000 bots are needed to support full CQ traffic.
Currently there are 200 bots in the fleet pool. So it should be suffcient
to support 2% traffic.

Bug: 997376
Change-Id: Ic7976aeb95646f8b92e2f66f5f5c4d41461ce87d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2333822Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Haiyang Pan <hypan@google.com>
Cr-Commit-Position: refs/heads/master@{#795050}

infra/config/generated/commit-queue.cfg

@@ -211,7 +211,9 @@ config_groups {
       }
       builders {
         name: "chromium/try/android-marshmallow-x86-rel"
-        includable_only: true
+        experiment_percentage: 2
+        location_regexp: ".*"
+        location_regexp_exclude: "infra/config/.+"
       }
       builders {
         name: "chromium/try/android-nougat-arm64-rel"

infra/config/generated/cq-builders.md

@@ -343,6 +343,9 @@ These builders are run on some percentage of builds. Their results are ignored
 by CQ. These are often used to test new configurations before they are added
 as required builders.
 
+* [android-marshmallow-x86-rel](https://ci.chromium.org/p/chromium/builders/try/android-marshmallow-x86-rel) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+android-marshmallow-x86-rel)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+android-marshmallow-x86-rel))
+  * Experiment percentage: 2
+
 * [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
 

infra/config/subprojects/chromium/try.star

@@ -124,6 +124,9 @@ try_.chromium_android_builder(
 try_.chromium_android_builder(
     name = "android-marshmallow-x86-rel",
     goma_jobs = goma.jobs.J150,
+    tryjob = try_.job(
+        experiment_percentage = 2,
+    ),
 )
 
 try_.chromium_android_builder(