[Cleanup] No need for extra boolean variable in FrameSelection::caretBlinkTimerFired.

The extra boolean variable is not needed. Removing it.

R=tkent@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/369673008

git-svn-id: svn://svn.chromium.org/blink/trunk@177503 bbb929c8-8fbe-4397-9dbb-9b2b20218538