Removed pinch viewport scroll offset distribution

The associated change in Blink makes the pinch viewport a proper
ScrollableArea meaning the normal path for synchronizing layer scroll
offsets is used.

This is a 2 sided patch, the other CL:
https://codereview.chromium.org/199253002/

BUG=349941

Review URL: https://codereview.chromium.org/210543002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@260105 0039d316-1c4b-4281-b951-d872f2087c98
gfx::Size LayerTreeHost::GetUIResourceSize(UIResourceId uid) const {
  UIResourceClientMap::const_iterator iter = ui_resource_client_map_.find(uid);
  if (iter == ui_resource_client_map_.end())
    return gfx::Size();

  const UIResourceClientData& data = iter->second;
  return data.size;
}

gfx::Size LayerTreeHost::GetUIResourceSize(UIResourceId uid) const {
  UIResourceClientMap::const_iterator iter = ui_resource_client_map_.find(uid);
  if (iter == ui_resource_client_map_.end())
    return gfx::Size();

  const UIResourceClientData& data = iter->second;
  return data.size;
}
