Clear button doesn't clear everything in memory section.

Clear all remaining measured information in order to restore the
timeline panel to the initial state.

R=loislo@chromium.org
BUG=341438

Review URL: https://codereview.chromium.org/163523002

git-svn-id: svn://svn.chromium.org/blink/trunk@167208 bbb929c8-8fbe-4397-9dbb-9b2b20218538