[DevTools] Add UMA for issues panel "Learn More" links

Frontend CL: https://crrev.com/c/2502288

Bug: chromium:1108501
Change-Id: I14fa19c8e9ee5c95ec5281e32dc9877f1678085d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2502428Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Wolfgang Beyer <wolfi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822097}

tools/metrics/histograms/enums.xml

@@ -16645,6 +16645,11 @@ metrics consent we also won't be able to send UMA metrics. -->
   <int value="5" label="HeavyAd Element opened"/>
   <int value="6" label="ContentSecurityPolicy Directive opened"/>
   <int value="7" label="ContentSecurityPolicy Element opened"/>
+  <int value="8" label="CrossOriginEmbedderPolicy LearnMore opened"/>
+  <int value="9" label="MixedContent LearnMore opened"/>
+  <int value="10" label="SameSiteCookie LearnMore opened"/>
+  <int value="11" label="HeavyAd LearnMore opened"/>
+  <int value="12" label="ContentSecurityPolicy LearnMore opened"/>
 </enum>
 
 <enum name="DevToolsKeybindSets">