Should not decode Wi-Fi QR code after onPause

Bug: 130141694
Test: manual
      atest WifiDppQrCodeScannerFragmentTest

Change-Id: I412fb7c06220c23bddc7b3c448fcc72a00bdecc3

src/com/android/settings/wifi/qrcode/QrCamera.java

@@ -401,4 +401,14 @@ public class QrCamera extends Handler {
             mScannerCallback.handleSuccessfulResult(qrCode.getText());
         }
     }
+
+    /**
+     * After {@link #start(SurfaceTexture)}, DecodingTask runs continuously to capture images and
+     * decode QR code. DecodingTask become null After {@link #stop()}.
+     *
+     * Uses this method in test case to prevent power consumption problem.
+     */
+    public boolean isDecodeTaskAlive() {
+        return mDecodeTask != null;
+    }
 }