Extract external file systems handling from isolated context.

content/content_tests.gypi

Index: content/content_tests.gypi
diff --git a/content/content_tests.gypi b/content/content_tests.gypi
index abf25464394ebfa0fa1d3ba2deab9e60674ab6f0..5f0ed492b78575e08d626a9947e6baa0fdc1991a 100644
--- a/content/content_tests.gypi
+++ b/content/content_tests.gypi
@@ -414,6 +414,7 @@
         '../webkit/dom_storage/dom_storage_database_unittest.cc',
         '../webkit/dom_storage/dom_storage_map_unittest.cc',
         '../webkit/dom_storage/session_storage_database_unittest.cc',
+        '../webkit/fileapi/external_mount_points_unittest.cc',
         '../webkit/fileapi/file_system_database_test_helper.cc',
         '../webkit/fileapi/file_system_database_test_helper.h',
         '../webkit/fileapi/file_system_directory_database_unittest.cc',
@@ -586,6 +587,9 @@
           'xcode_settings': {'OTHER_LDFLAGS': ['-Wl,-ObjC']},
         }],
         ['chromeos==1', {
+          'sources': [
+              '../webkit/chromeos/fileapi/cros_mount_point_provider_unittest.cc'

[jam, 2013/01/14 21:05:46]

you should list this file path above. by convention targets should include files
for all platforms, then exclude them when they need to be excluded. this keeps
all the files visible in each platform's IDE. also in this case, you wouldn't
need to exclude it since the path includes chromeos, which means that the
filename filters should automatically do this

[tbarzic, 2013/01/14 21:36:28]

Done.

+          ],
           'sources/': [
             ['exclude', '^browser/renderer_host/gtk_key_bindings_handler_unittest.cc'],
           ],