cc: Initialize PageScaleAnimation's start time on first animation

This removes the possibility that creating a PageScaleAnimation
will initialize the animation time before the BeginFrame on the
impl thread arrives, introducing unwanted jitter.

BUG=297631

Review URL: https://codereview.chromium.org/24502002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225487 0039d316-1c4b-4281-b951-d872f2087c98
8 files changed