CCA: Select the best one if there are multiple QR codes detected

This CL shows the content of the QR code that is closet to the center of
the camera frame if there are multiple QR codes detects.

Bug: b/172879638
Test: Manually with two QR codes
Change-Id: I236bf0a5652b67339051bb3603011209464de6f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2631549
Commit-Queue: Inker Kuo <inker@chromium.org>
Reviewed-by: Inker Kuo <inker@chromium.org>
Auto-Submit: Shik Chen <shik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844002}

chromeos/components/camera_app_ui/resources/js/models/barcode_worker.js

@@ -33,8 +33,29 @@ class BarcodeWorker {
       return null;
     }
 
-    // TODO(b/172879638): Handle multiple barcodes.
-    return codes[0].rawValue;
+    const cx = bitmap.width / 2;
+    const cy = bitmap.height / 2;
+    /**
+     * @param {!DetectedBarcode} code
+     * @return {number}
+     */
+    const distanceToCenter = (code) => {
+      const {left, right, top, bottom} = code.boundingBox;
+      const x = (left + right) / 2;
+      const y = (top + bottom) / 2;
+      return Math.hypot(x - cx, y - cy);
+    };
+
+    let bestCode = codes[0];
+    let minDistance = distanceToCenter(codes[0]);
+    for (let i = 1; i < codes.length; i++) {
+      const distance = distanceToCenter(codes[i]);
+      if (distance < minDistance) {
+        bestCode = codes[i];
+        minDistance = distance;
+      }
+    }
+    return bestCode.rawValue;
   }
 }