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
 void LayerTreeHost::StartRateLimiter() {
   if (animating_)
     return;

  if (!rate_limit_timer_.IsRunning()) {
    rate_limit_timer_.Start(FROM_HERE,
                            base::TimeDelta(),
                            this,
                            &LayerTreeHost::RateLimit);
  }
}

 void LayerTreeHost::StartRateLimiter() {
   if (animating_)
     return;

  if (!rate_limit_timer_.IsRunning()) {
    rate_limit_timer_.Start(FROM_HERE,
                            base::TimeDelta(),
                            this,
                            &LayerTreeHost::RateLimit);
  }
}
