Set testonly to true for targets that depends on base_java_test_support

components/precache/android/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/rules.gni")
 
 # GYP: //components/precache.gypi:precache_java
 android_library("precache_java") {
   deps = [
     "//base:base_java",
   ]
   java_files = [
     "java/src/org/chromium/components/precache/DeviceState.java",
     "java/src/org/chromium/components/precache/NetworkInfoDelegate.java",
     "java/src/org/chromium/components/precache/NetworkInfoDelegateFactory.java",
   ]
 }
 
 android_library("precache_javatests") {
+  testonly = true
   deps = [
     ":precache_java",
     "//base:base_java_test_support",
   ]
   java_files = [
     "javatests/src/org/chromium/components/precache/DeviceStateTest.java",
     "javatests/src/org/chromium/components/precache/MockDeviceState.java",
   ]
 }