Prevent submitting URL Metric if viewport size changed

plugins/optimization-detective/detect.js

@@ -127,6 +127,12 @@ function recursiveFreeze( obj ) {
 	Object.freeze( obj );
 }
 
+// This needs to be captured early in case the user later resizes the window.
+const viewport = {
+	width: win.innerWidth,
+	height: win.innerHeight,
+};
+
 /**
  * URL Metric being assembled for submission.
  *
@@ -442,10 +448,7 @@ export default async function detect( {
 
 	urlMetric = {
 		url: currentUrl,
-		viewport: {
-			width: win.innerWidth,
-			height: win.innerHeight,
-		},
+		viewport,
 		elements: [],
 	};
 
@@ -506,6 +509,20 @@ export default async function detect( {
 		);
 	} );
 
+	// Only proceed with submitting the URL Metric if viewport stayed the same size. Changing the viewport size (e.g. due
+	// to resizing a window or changing the orientation of a device) will result in unexpected metrics being collected.
+	if (
+		window.innerWidth !== urlMetric.viewport.width ||
+		window.innerHeight !== urlMetric.viewport.height
+	) {
+		if ( isDebug ) {
+			log(
+				'Aborting URL Metric collection due to viewport size change.'
+			);
+		}
+		return;
+	}
+
 	if ( extensions.size > 0 ) {
 		for ( const [
 			extensionModuleUrl,