Add @UsedByReflection to PiiElider.

This is accessed by native and must not be renamed by proguard.
BUG=905960

Change-Id: I99f74affe95c2e9356f66303eb921fa8a5eb1125
Reviewed-on: https://chromium-review.googlesource.com/c/1340366Reviewed-by: agrieve <agrieve@chromium.org>
Reviewed-by: Sam Maier <smaier@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Commit-Queue: Yaron Friedman <yfriedman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608883}

base/android/java/src/org/chromium/base/PiiElider.java

@@ -7,6 +7,8 @@ package org.chromium.base;
 import android.text.TextUtils;
 import android.util.Patterns;
 
+import org.chromium.base.annotations.UsedByReflection;
+
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -171,6 +173,7 @@ public class PiiElider {
      * @param stacktrace Multiline stacktrace as a string.
      * @return Stacktrace with elided URLs.
      */
+    @UsedByReflection("jni_android.cc")
     public static String sanitizeStacktrace(String stacktrace) {
         String[] frames = stacktrace.split("\\n");
         // Sanitize first stacktrace line which contains the exception message.