Don't set sent_top_controls_delta when root layer doesn't exist.
Soon after CC initialization when the layer tree doesn't exist yet, the
top controls delta can still be set. In that case, an early return in
LTH::ApplyScrollAndScale doesn't forward the value to Blink -- the
"sent_" value is misleading here, and this causes the delta to get
clobbered on the next commit. Avoid this scenario by matching the
LTH-side early-return in LTHI.
NOTRY=true
BUG=423139
Review URL: https://codereview.chromium.org/647753004
Cr-Commit-Position: refs/heads/master@{#299426}
3 files changed
