Added UnguessableToken.java .

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index a3e3205eae9f137c15c774fdff736a88124201f8..c55a15d4bdb5d6d8a7667b886fca084a79f4b783 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -185,6 +185,8 @@ component("base") {
     "android/jni_registrar.h",
     "android/jni_string.cc",
     "android/jni_string.h",
+    "android/jni_unguessable_token.cc",
+    "android/jni_unguessable_token.h",
     "android/jni_utils.cc",
     "android/jni_utils.h",
     "android/jni_weak_ref.cc",
@@ -1746,6 +1748,7 @@ test("base_unittests") {
     "android/jni_android_unittest.cc",
     "android/jni_array_unittest.cc",
     "android/jni_string_unittest.cc",
+    "android/jni_unguessable_token_unittest.cc",
     "android/library_loader/library_prefetcher_unittest.cc",
     "android/path_utils_unittest.cc",
     "android/scoped_java_ref_unittest.cc",
@@ -2232,6 +2235,7 @@ if (is_android) {
       "android/java/src/org/chromium/base/SystemMessageHandler.java",
       "android/java/src/org/chromium/base/ThreadUtils.java",
       "android/java/src/org/chromium/base/TraceEvent.java",
+      "android/java/src/org/chromium/base/UnguessableToken.java",
       "android/java/src/org/chromium/base/library_loader/LibraryLoader.java",
       "android/java/src/org/chromium/base/metrics/RecordHistogram.java",
       "android/java/src/org/chromium/base/metrics/RecordUserAction.java",
@@ -2305,6 +2309,7 @@ if (is_android) {
       "android/java/src/org/chromium/base/SystemMessageHandler.java",
       "android/java/src/org/chromium/base/ThreadUtils.java",
       "android/java/src/org/chromium/base/TraceEvent.java",
+      "android/java/src/org/chromium/base/UnguessableToken.java",
       "android/java/src/org/chromium/base/VisibleForTesting.java",
       "android/java/src/org/chromium/base/annotations/AccessedByNative.java",
       "android/java/src/org/chromium/base/annotations/CalledByNative.java",