Restore backspace and shift-backspace as accelerators on ChromeOS.
Restore backspace and shift-backspace as accelerators on ChromeOS.

CROSBUG=4348
TEST=Backspace navigates back
Review URL: http://codereview.chromium.org/2863027

git-svn-id: http://src.chromium.org/svn/trunk/src@50996 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: c10e735bbce26fa9e824b3546e8e11db4aca2c9f
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser