Use ScrollOffset instead of vector2d to track scroll offset in cc

This is for preparing converting blink side scroll offset to be double
type. Assuming blink side starts to use double scroll offset, it can
be passed back from main/blink to compositor without converting to int
type.

BUG=414283

Review URL: https://codereview.chromium.org/584503005

Cr-Commit-Position: refs/heads/master@{#297692}


CrOS-Libchrome-Original-Commit: f57925d399f2eda19fdaab9191257e51a3af04a0
5 files changed
tree: cc905479d174b324237ed04174462c4b97218061
  1. base/
  2. build/
  3. components/
  4. dbus/
  5. device/
  6. ipc/
  7. mojo/
  8. testing/
  9. third_party/
  10. ui/