After histrogram timer added time recaling functionality,
some events, e.g. parse, histogram timer generates event log ending with 'MicroSeconds'.

Since ProfViz can't recorgnize it, this patch cuts off 'MicroSeconds' postfix.

R=vogelheim@chromium.org, yangguo@chromium.org
BUG=chromium:
LOG=N

Review URL: https://codereview.chromium.org/1771293002

Cr-Commit-Position: refs/heads/master@{#34710}