Update from https://crrev.com/318214

build/jar_file_jni_generator.gypi

 # Copyright (c) 2012 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.
 
 # This file is meant to be included into a target to provide a rule
 # to generate jni bindings for system Java-files in a consistent manner.
 #
 # To use this, create a gyp target with the following form:
 # {
 #   'target_name': 'android_jar_jni_headers',
 #   'type': 'none',
 #   'variables': {
 #     'jni_gen_package': 'chrome',
 #     'input_java_class': 'java/io/InputStream.class',
 #   },
 #   'includes': [ '../build/jar_file_jni_generator.gypi' ],
 # },
 #
 # Optional variables:
 #  input_jar_file - The input jar file, if omitted, android_sdk_jar will be used.
 
 {
   'variables': {
     'jni_generator': '<(DEPTH)/base/android/jni_generator/jni_generator.py',
     # A comma separated string of include files.
     'jni_generator_includes%': (
         'base/android/jni_generator/jni_generator_helper.h'
     ),
-    'native_exports%': '',
+    'native_exports%': '--native_exports_optional',
   },
   'actions': [
     {
       'action_name': 'generate_jni_headers_from_jar_file',
       'inputs': [
         '<(jni_generator)',
         '<(input_jar_file)',
         '<(android_sdk_jar)',
       ],
       'variables': {
@@ skipping 26 matching lines @@
   'hard_dependency': 1,
   'conditions': [
     ['android_webview_build==1', {
       'variables': {
         'native_exports%': '--native_exports',
       },
       'dependencies': [
         '<(DEPTH)/build/android/android_exports.gyp:android_exports',
       ],
     }],
-    ['clang==0', {
-      # Clang builds currently fail with --native_exports_optional due to
-      # http://llvm.org/bugs/show_bug.cgi?id=22602 - only enable for gcc.
-      # http://crbug.com/442327
-      'variables': {
-        'native_exports%': '--native_exports_optional',
-      },
-    }],
   ],
 }