android: Hide JNI exports by default.

build/android/android_exports.gyp

 # 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.
 
+# This target is only used when android_webview_build==1 - it implements a
+# whitelist for exported symbols to minimise the binary size and prevent us
+# accidentally exposing things we don't mean to expose.
+
 {
+  'variables': {
+    'android_linker_script%': '<(SHARED_INTERMEDIATE_DIR)/android_webview_export_whitelist.lst',
+  },
   'targets': [
     {
       'target_name': 'android_exports',

[rmcilroy, 2015/02/03 13:43:56]

nit - could we rename this gyp file / target to android_webview_exports for
clarity?

       'type': 'none',
       'inputs': [
-        '<(DEPTH)/build/android/android_exports.lst',
+        '<(DEPTH)/build/android/android_webview_export_whitelist.lst',
       ],
       'outputs': [
         '<(android_linker_script)',
       ],
       'copies': [
         {
           'destination': '<(SHARED_INTERMEDIATE_DIR)',
           'files': [
             '<@(_inputs)',
          ],
         },
       ],
       'conditions': [
         ['component=="static_library"', {
           'link_settings': {
             'ldflags': [
               # Only export symbols that are specified in version script.
               '-Wl,--version-script=<(android_linker_script)',
             ],
-            'ldflags!': [
-              '-Wl,--exclude-libs=ALL',
-            ],
           },
         }],
       ],
     },
   ],
 }