Add use counters for MouseEvent.screen[XY]

These are equivalent to window.screen[XY], which were measured in
https://chromium-review.googlesource.com/c/chromium/src/+/1384047.

Bug: 915620, 1016935
Change-Id: Iddfee602c9ffd4a360fa5bbca8a0366382c579d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1874594
Commit-Queue: David Benjamin <davidben@chromium.org>
Auto-Submit: David Benjamin <davidben@chromium.org>
Reviewed-by: Yoav Weiss <yoavweiss@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709990}

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

@@ -2453,6 +2453,8 @@ enum WebFeature {
   kMovedOrResizedPopup = 3069,
   kMovedOrResizedPopup2sAfterCreation = 3070,
   kDOMWindowOpenPositioningFeatures = 3071,
+  kMouseEventScreenX = 3072,
+  kMouseEventScreenY = 3073,
 
   // 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/events/mouse_event.idl

@@ -24,8 +24,8 @@
     ConstructorCallWith=ScriptState,
     Exposed=Window
 ] interface MouseEvent : UIEvent {
-    readonly attribute double           screenX;
-    readonly attribute double           screenY;
+    [HighEntropy, MeasureAs=MouseEventScreenX] readonly attribute double screenX;
+    [HighEntropy, MeasureAs=MouseEventScreenY] readonly attribute double screenY;
     readonly attribute double           clientX;
     readonly attribute double           clientY;
     readonly attribute boolean          ctrlKey;

tools/metrics/histograms/enums.xml

@@ -25194,6 +25194,8 @@ Called by update_net_error_codes.py.-->
   <int value="3069" label="MovedOrResizedPopup"/>
   <int value="3070" label="MovedOrResizedPopup2sAfterCreation"/>
   <int value="3071" label="DOMWindowOpenPositioningFeatures"/>
+  <int value="3072" label="MouseEventScreenX"/>
+  <int value="3073" label="MouseEventScreenY"/>
 </enum>
 
 <enum name="FeaturePolicyAllowlistType">