Add a UseCounter for inline relative MouseEvent offsets

The UseCounter is counted when offsetX/offsetY/layerX/layerY
is requested, and the target element is rendered inline.

Bug: 1054515
Change-Id: Ie584a9070edce2748537edd06b8b8f2f27efe0c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2517020Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823607}

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

@@ -3046,7 +3046,7 @@ enum WebFeature {
   kCSSPseudoHostContextCompoundList = 3717,
   kCSSPseudoHostDynamicSpecificity = 3718,
   kGetCurrentBrowsingContextMedia = 3719,
-
+  kMouseEventRelativePositionForInlineElement = 3720,
   // Add new features immediately above this line. Don't change assigned
   // numbers of any item, and don't reuse removed slots.
   // Also, run update_use_counter_feature_enum.py in

third_party/blink/renderer/core/events/mouse_event.cc

@@ -491,6 +491,12 @@ void MouseEvent::ComputeRelativePosition() {
     FloatPoint local_pos = layout_object->AbsoluteToLocalFloatPoint(
         FloatPoint(AbsoluteLocation()));
 
+    if (layout_object->IsInline()) {
+      UseCounter::Count(
+          target_node->GetDocument(),
+          WebFeature::kMouseEventRelativePositionForInlineElement);
+    }
+
     // Adding this here to address crbug.com/570666. Basically we'd like to
     // find the local coordinates relative to the padding box not the border
     // box.

tools/metrics/histograms/enums.xml

@@ -30133,6 +30133,7 @@ Called by update_use_counter_feature_enum.py.-->
   <int value="3717" label="CSSPseudoHostContextCompoundList"/>
   <int value="3718" label="CSSPseudoHostDynamicSpecificity"/>
   <int value="3719" label="GetCurrentBrowsingContextMedia"/>
+  <int value="3720" label="MouseEventRelativePositionForInlineElement"/>
 </enum>
 
 <enum name="FeaturePolicyAllowlistType">