Fix hidden experiments shortcut on Linux

keyIdentifier returns "U+00A0" on Linux not "Shift".

BUG=None

Review URL: https://codereview.chromium.org/295653002

git-svn-id: svn://svn.chromium.org/blink/trunk@174281 bbb929c8-8fbe-4397-9dbb-9b2b20218538