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 375a32747b95902452ea3be5c455147e4d562d1c..4f07743209640de6b8f55dda25eede7d96a470c0 100644
--- a/content/content_tests.gypi
+++ b/content/content_tests.gypi
@@ -413,6 +413,7 @@
         '../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',
@@ -584,6 +585,9 @@
           'xcode_settings': {'OTHER_LDFLAGS': ['-Wl,-ObjC']},
         }],
         ['chromeos==1', {
+          'sources': [
+              '../webkit/chromeos/fileapi/cros_mount_point_provider_unittest.cc'
+          ],
           'sources/': [
             ['exclude', '^browser/renderer_host/gtk_key_bindings_handler_unittest.cc'],
           ],