Make CastSysInfoAndroid.getSerialNumber() public.

Bug: 142062297
Test: With internal patch, view Cast settings UI on emulator
Merge-With: eureka-internal/322486

Change-Id: I91ab48f651c998bcdc0456d8c4a2bd6911bf1d55
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1846017Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Simeon Anfinrud <sanfin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703560}

chromecast/browser/android/apk/src/org/chromium/chromecast/shell/CastSysInfoAndroid.java

@@ -19,7 +19,7 @@ public final class CastSysInfoAndroid {
 
     @SuppressLint("HardwareIds")
     @CalledByNative
-    private static String getSerialNumber() {
+    public static String getSerialNumber() {
         if (!Build.SERIAL.equals(Build.UNKNOWN)) return Build.SERIAL;
         return CastSerialGenerator.getGeneratedSerial();
     }