cherry-pick from oc-dev: docs: Note regarding device IDs, Build.java

Added note within getSerial() in android.os.Build class. Device
identifiers, such as hardware serial numbers, can be modified if a
device is rooted. Others can use key attestation to discover these
changes. Added a note to this effect within this method.

Test: make ds-docs -j8

Bug: 38312326
Change-Id: I76e3f6a15b9a8673ca3304218653e8cd26da38d7
Original-Change-Id: Ibd2dab621c14683e12a213957b567ee49b8d00fd

core/java/android/os/Build.java

@@ -117,8 +117,14 @@ public class Build {
     public static final String SERIAL = getString("no.such.thing");
 
     /**
-     * Gets the hardware serial, if available.
-     * @return The serial if specified.
+     * Gets the hardware serial number, if available.
+     *
+     * <p class="note"><b>Note:</b> Root access may allow you to modify device identifiers, such as
+     * the hardware serial number. If you change these identifiers, you can use
+     * <a href="/training/articles/security-key-attestation.html">key attestation</a> to obtain
+     * proof of the device's original identifiers.
+     *
+     * @return The serial number if specified.
      */
     @RequiresPermission(Manifest.permission.READ_PHONE_STATE)
     public static String getSerial() {