Measure usage of `<frameset>`.

Change-Id: I2cd3b65e477a99a3e7c2368767958d0f08156a42
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1764156Reviewed-by: Eric Lawrence [MSFT] <ericlaw@microsoft.com>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#689449}

third_party/blink/public/mojom/web_feature/web_feature.mojom

@@ -2384,6 +2384,7 @@ enum WebFeature {
   kWakeLockAcquireSystemLock = 3006,
   kThirdPartyServiceWorker = 3007,
   kJSSelfProfiling = 3008,
+  kHTMLFrameSetElement = 3009,
 
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.

third_party/blink/renderer/core/html/html_frame_set_element.cc

@@ -50,6 +50,7 @@ HTMLFrameSetElement::HTMLFrameSetElement(Document& document)
       frameborder_set_(false),
       noresize_(false) {
   SetHasCustomStyleCallbacks();
+  UseCounter::Count(document, WebFeature::kHTMLFrameSetElement);
 }
 
 bool HTMLFrameSetElement::IsPresentationAttribute(

tools/metrics/histograms/enums.xml

@@ -24364,6 +24364,7 @@ Called by update_net_error_codes.py.-->
   <int value="3006" label="WakeLockAcquireSystemLock"/>
   <int value="3007" label="ThirdPartyServiceWorker"/>
   <int value="3008" label="JSSelfProfiling"/>
+  <int value="3009" label="HTMLFrameSetElement"/>
 </enum>
 
 <enum name="FeaturePolicyAllowlistType">