Vibration cannot be canceled during pattern vibration.

Vibration could not be canceled during pattern vibration is working.
In the resting time which are even numbers of pattern,
 m_isVibrating will be false and cancel will thus return early.
WebKit bug : https://bugs.webkit.org/show_bug.cgi?id=117822

BUG=222504,261467,310137

Review URL: https://codereview.chromium.org/18478003

git-svn-id: svn://svn.chromium.org/blink/trunk@160289 bbb929c8-8fbe-4397-9dbb-9b2b20218538