luci: increase the experimental percentage to 40 from 20 for MM-x86-rel

The pool has plenty of 4-cores for extra builds: http://shortn/_Bdez2rvyhe

Bug: 997376, 1127110
Change-Id: I04a4a1da5bcd143ba8e653dae52dfd6df8df6419
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2444050
Auto-Submit: Haiyang Pan <hypan@google.com>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812982}

infra/config/generated/commit-queue.cfg

@@ -239,7 +239,7 @@ config_groups {
       }
       builders {
         name: "chromium/try/android-marshmallow-x86-rel"
-        experiment_percentage: 20
+        experiment_percentage: 40
         location_regexp: ".*"
         location_regexp_exclude: ".+/[+]/docs/.+"
         location_regexp_exclude: ".+/[+]/infra/config/.+"

infra/config/generated/cq-builders.md

@@ -348,7 +348,7 @@ 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: 20
+  * Experiment percentage: 40
 
 * [android-pie-arm64-rel](https://ci.chromium.org/p/chromium/builders/try/android-pie-arm64-rel) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+android-pie-arm64-rel)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+android-pie-arm64-rel))
   * Experiment percentage: 60

infra/config/subprojects/chromium/try.star

@@ -265,7 +265,7 @@ try_.chromium_android_builder(
     goma_jobs = goma.jobs.J300,
     ssd = True,
     tryjob = try_.job(
-        experiment_percentage = 20,
+        experiment_percentage = 40,
     ),
 )