Use the new java_cpp_enum rule in content.

build/config/android/rules.gni

 # 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/android/config.gni")
 import("//build/config/android/internal_rules.gni")
 import("//tools/grit/grit_rule.gni")
 
 assert(is_android)
 
@@ skipping 283 matching lines @@
 #       "org/chromium/FooEnum.java",
 #     ]
 #   }
 template("java_cpp_enum") {
   if (defined(invoker.testonly)) { testonly = invoker.testonly }
 
   assert(defined(invoker.sources))
   assert(defined(invoker.outputs))
 
   action("${target_name}__generate_enum") {
-    sources = rebase_path(invoker.sources, root_build_dir)
+    sources = invoker.sources
     script = "//build/android/gyp/java_cpp_enum.py"
     gen_dir = "${target_gen_dir}/${target_name}/enums"
     outputs = get_path_info(
         rebase_path(invoker.outputs, ".", gen_dir), "abspath")
 
     args = [
       "--output_dir", rebase_path(gen_dir, root_build_dir),
     ]
     foreach(output, rebase_path(outputs, root_build_dir)) {
       args += ["--assert_file", output]
     }
-    args += sources
+    args += rebase_path(invoker.sources, root_build_dir)
   }
 
   generate_enum_outputs = get_target_outputs(":${target_name}__generate_enum")
   base_gen_dir = get_label_info(":${target_name}__generate_enum",
                                 "target_gen_dir")
 
   srcjar_path = "${target_gen_dir}/${target_name}.srcjar"
   zip("${target_name}__zip_srcjar") {
     inputs = generate_enum_outputs
     output = srcjar_path
@@ skipping 757 matching lines @@
     args = [
       "--files=$rebased_binaries_list",
       "--files=@FileArg($rebased_libraries_list:libraries)",
     ]
   }
 
   group(target_name) {
     deps = final_deps
   }
 }