Manually update trunk VERSION from 3407.0 to 3408.0

This brings things back in sync after a failed branching.

TBR=govind@google.com
NOTRY=true

Bug: 825063
Change-Id: Ia1b98d068b6c38cc1bb0337abe9492e723c8e70d
Reviewed-on: https://chromium-review.googlesource.com/1028611Reviewed-by: Michael Moss <mmoss@chromium.org>
Commit-Queue: Michael Moss <mmoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553673}

chrome/VERSION

 MAJOR=68
 MINOR=0
-BUILD=3407
+BUILD=3408
 PATCH=0