Simplify how variable_map is initialized. Suggestion by thakis@chromium.org.
Simplify how variable_map is initialized. Suggestion by thakis@chromium.org.

BUG=https://code.google.com/p/grit-i18n/issues/detail?id=23

Review URL: https://codereview.chromium.org/122253002
imuse2012/grit-i18n,imuse2012/grit-i18n,camny125/grit-i18n,camny125/grit-i18n