DevTools: Make 'Preserve Log Upon Navigation' consistent between Network and Console

The Network panel of devtools shows a checkbox to preserve the log when
the user reloads or navigates. The Console panel has a similar option,
except hidden in a context menu.

This patch makes the Console panel UI match the Network panel by adding
the checkbox and removing the context menu item.

BUG=119643

Review URL: https://codereview.chromium.org/361653002

git-svn-id: svn://svn.chromium.org/blink/trunk@177242 bbb929c8-8fbe-4397-9dbb-9b2b20218538