Explicitly declare mojo_application_base->mojom dep in gyp

mojo/public/cpp/application/application_connection.h includes
service_provider.mojom.h, so it must explicitly declare a hard
dependency in gyp on the mojom target that produces this header or the
header might not exist on disk when targets that include
application_connection.h are compiled. This does so by exporting
the application_bindings_mojom dependent settings (which includes the
hard_dependency bit) from mojo_application_bindings, which
mojo_application_base depends on and exports.

R=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/733513003