DevTools: set deviceTextAutosizing emulation defaults to 'false'.

TBR=dgozma
NOTRY=true

Review URL: https://codereview.chromium.org/347253002

git-svn-id: svn://svn.chromium.org/blink/trunk@176683 bbb929c8-8fbe-4397-9dbb-9b2b20218538