DevTools: Add APCA experiment

Bug: 1121900
Change-Id: Ia64736ac414b08c4999a9ff077bf82c0e31d03f6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2534830Reviewed-by: Mathias Bynens <mathias@chromium.org>
Commit-Queue: Alex Rudenko <alexrudenko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826851}

tools/metrics/histograms/enums.xml

@@ -16693,6 +16693,7 @@ metrics consent we also won't be able to send UMA metrics. -->
   <int value="36" label="cssFlexboxFeatures"/>
   <int value="37" label="showWebVitalsInPerformancePanel"/>
   <int value="38" label="recorder"/>
+  <int value="39" label="APCA"/>
 </enum>
 
 <enum name="DevToolsGridOverlayOpenedFrom">