[Android] Include NestedSystemMessageHandler in gn builds of content_shell_apk.

content/test/BUILD.gn

 # Copyright 2014 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/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build_overrides/v8.gni")
@@ skipping 304 matching lines @@
 
     #"//content/shell:content_shell_lib",
     "//content/renderer:for_content_tests",
     "//mojo/edk/test:test_support",
     "//skia",
     "//ui/accessibility:ax_gen",
     "//v8",
   ]
 
   if (is_android) {
-    deps += [ ":jni" ]
+    deps += [ "//content/public/test/android:test_support_content_jni_headers" ]
   }
 }
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 
-  generate_jni("jni") {
-    sources = [
-      "../public/test/android/javatests/src/org/chromium/content/browser/test/NestedSystemMessageHandler.java",
-    ]
-    jni_package = "content/public/test"
-  }
-}
-
-if (is_android) {
   jinja_template("content_browsertests_manifest") {
     testonly = true
     input =
         "//content/shell/android/browsertests_apk/AndroidManifest.xml.jinja2"
     output =
         "${target_gen_dir}/content_browsertests_manifest/AndroidManifest.xml"
   }
 
   android_library("content_browsertests_java") {
     testonly = true
@@ skipping 591 matching lines @@
         "//gpu:test_support",
         "//media/base/android",
         "//media/base/android:media_java",
         "//media/capture/video/android:capture_java",
         "//testing/gmock",
         "//ui/android:ui_java",
       ]
     }
   }
 }