Added UnguessableToken.java .

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index a3e3205eae9f137c15c774fdff736a88124201f8..f4ee65bbb974318cb71bced12eab43c199ee81ec 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -214,6 +214,8 @@ component("base") {
     "android/sys_utils.h",
     "android/trace_event_binding.cc",
     "android/trace_event_binding.h",
+    "android/unguessable_token_android.cc",
+    "android/unguessable_token_android.h",
     "at_exit.cc",
     "at_exit.h",
     "atomic_ref_count.h",
@@ -1750,6 +1752,7 @@ test("base_unittests") {
     "android/path_utils_unittest.cc",
     "android/scoped_java_ref_unittest.cc",
     "android/sys_utils_unittest.cc",
+    "android/unguessable_token_android_unittest.cc",
     "at_exit_unittest.cc",
     "atomicops_unittest.cc",
     "barrier_closure_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",