PDF Plugin: Swallow Invalidate calls before getting initial size
The PDF Plugin current expects the size to be set before any invalidate operations, and will DCHECK that.
https://crrev.com/323331 broke this, as the initial size is given to the plugin is now deferred to give the DOM a chance to 'settle down'.
Instead, we can just ignore invalidate calls before the size is set. When the size is actually set, the whole page will be invalidated anyways, so there's no harm.
BUG=474428
Review URL: https://codereview.chromium.org/
1067043002
Cr-Commit-Position: refs/heads/master@{#324947}