Adding use_gnome_keyring=1 to GYP_DEFINES and compiling (eventually) yields the following on my FreeBSD 10.0-RELEASE-p12 system with a recent ports tree:

In file included from ../../chrome/browser/password_manager/password_store_factory.cc:37:
../../chrome/browser/password_manager/native_backend_gnome_x.h:65:31: error: no member named 'gnome_keyring_attribute_list_new' in the global namespace; did you mean 'gnome_keyring_attribute_list_free'?
  GNOME_KEYRING_FOR_EACH_FUNC(GNOME_KEYRING_DECLARE_POINTER)
                              ^
../../chrome/browser/password_manager/native_backend_gnome_x.h:59:42: note: expanded from macro 'GNOME_KEYRING_FOR_EACH_FUNC'
  GNOME_KEYRING_FOR_EACH_NON_MOCKED_FUNC(F)        \
                                         ^
../../chrome/browser/password_manager/native_backend_gnome_x.h:55:3: note: expanded from macro 'GNOME_KEYRING_FOR_EACH_NON_MOCKED_FUNC'
  F(attribute_list_new)                            \
  ^
../../chrome/browser/password_manager/native_backend_gnome_x.h:64:22: note: expanded from macro 'GNOME_KEYRING_DECLARE_POINTER'
    static typeof(&::gnome_keyring_##name) gnome_keyring_##name;
                   ~~^  
<scratch space>:181:1: note: expanded from here
gnome_keyring_attribute_list_new
^
/usr/local/include/gnome-keyring-1/gnome-keyring.h:136:28: note: 'gnome_keyring_attribute_list_free' declared here
void                       gnome_keyring_attribute_list_free          (GnomeKeyringAttributeList *attributes);
                           ^
1 error generated.
ninja: build stopped: subcommand failed.
===> Compilation failed unexpectedly.
Try to set MAKE_JOBS_UNSAFE=yes and rebuild before reporting the failure to
the maintainer.
*** Error code 1

Stop.
make: stopped in /usr/ports/www/chromium
===>  Cleaning for chromium-38.0.2125.111


This makes it impossible to use gnome-keyring to store encrypted passwords for chromium on FreeBSD, which is very unfortunate.

Seeing as building on FreeBSD isn't officially supported by the chromium team, I suppose this is the best place to report this bug.