DevTools: remove isTrusted check and isUserGesture from ViewportControl

Previously, the ViewportControl never stuck to the bottom after a scroll event.
The event.isTrusted check was always true, so it was not correctly
distinguishing user-generated scroll events from script-generated ones.  This
CL removes isUserGesture accordingly.

BUG=613879

Review-Url: https://codereview.chromium.org/2154893002
Cr-Commit-Position: refs/heads/master@{#407062}
4 files changed